Power-supply apparatus

ABSTRACT

A power supply apparatus includes a controller that performs the following action. The controller determines a target direct-current electric amount value in accordance with an external input. Then, the controller performs feedback control in such a manner that an amount of direct-current electric power input to an inverter reaches the target direct-current electric amount value.

TECHNICAL FIELD

The present invention relates to a power supply apparatus capable ofoutputting alternating-current electric power to a plasma generator(capacitive load apparatus) that can generate an ozone gas and a radicalgas and controlling the output alternating-current electric power.

BACKGROUND ART

In general, a plasma generator being a capacitive load apparatus thatgenerates a large amount of ozone gas and a large amount of radical gasincludes a plurality of discharge cells connected in parallel. Eachdischarge cell includes a pair of electrodes opposed to each other toform a discharge space with a dielectric located between the electrodes.In recent years, a very-large-scale plasma generator is in increasingdemand which includes laminations or blocks of a plurality of dischargecells connected in parallel. With a source gas being supplied in thedischarge space in the plasma generator, a power supply apparatusapplies an alternating-current high voltage between the discharge cells.The gas in the discharge space is excited by an electric field caused bythe application of the voltage, generating a large amount of ozone gasand a large amount of radical gas.

The generated ozone gas and the generated radical gas often find use asa film deposition gas for a functional film such as an oxide insulatingfilm or as a cleaning gas for components mainly in the semiconductormanufacturing field, the solar photovoltaic panel manufacturing field,and the flat display manufacturing field. In these fields which requiresthe ozone gas and the radical gas, these gases need to be supplied inlarge quantities and need to be supplied stably at high concentrationsand high purities on a 24-hour basis while the amount and theconcentrations of these gases that are generated and output need to becontrolled stably and easily.

In general, loads driven due to the application of alternating-currentvoltage includes, besides a resistive (R) load such as a thermoelectricapparatus, an inductive (L) load such as a motor load and a capacitive(C) load associated with apparatuses that accumulate electric chargesand apply a high voltage. Apart from the resistive (R) load such as thethermoelectric apparatuses, the inductive (L) load such as the motorload generally has constant impedance, and accordingly the electricpower input increases in proportion to the increasing rate of voltagesupplied from the power source to the load. Thus, the inductive load isrelatively stable. In contrast, the capacitive load apparatus (C) suchas a plasma generator is a nonlinear load that has inconstant impedance,which varies depending on the load conditions. Thus, it is verydifficult to stably operate the plasma generator by supplying a voltagefrom the power supply apparatus. This is more likely to cause thebreakage and the like of the discharge cell portion in the conventionalplasma generator. It is therefore difficult to stably operate the plasmagenerator for a long period of time through the use of the voltage fromthe power supply apparatus.

The application of alternating current to a load being an inductive loador a capacitive load causes a phase lag or a phase lead of a loadcurrent Id relative to an applied load voltage Vd. Consequently, theratio (load power factor ηd=PW/PQ) of an actually supplied electricpower capacity PQ (=Vd×Id) to an active power PW supplied to the loadbecomes extremely small. Increasing the active power PW of a powersupply apparatus having a small load power factor ηd requires thegreater electric power capacity PQ (=Vd×Id), and thus a very-large-scalepower supply apparatus needs to be installed.

For a smaller power supply apparatus, a power factor improvementapparatus (power factor improvement means) has been known which ismounted on the output unit of the power supply apparatus for improvementof the power factor ηd. The different power factor improvementapparatuses are provided for an inductive load and a capacitive load.The power factor improvement apparatus for the inductive load is acapacitor bank, which is provided to improve the L load. The powerfactor improvement apparatus for the capacitive load is a reactor, whichis provided to improve the C load. The power supply apparatus worksthrough the use of the inductive load (or the capacitive load) and thepower factor improvement apparatus at around an alternating-currentvoltage frequency fc (resonance frequency) that creates the resonancestate between the load and the power supply apparatus.

The resonance frequency fc is given by fc=½·π·(L·C)^(0.5) (hereinafterreferred to as Expression (1)).

For the inductive load, substituting the capacitor bank being the powerfactor improvement apparatus into C of Expression (1) yields theresonance frequency fc. For the capacitive load, substituting thereactor Lp being the power factor improvement apparatus into L ofExpression (1) yields the resonance frequency fc. The power supplyapparatus works on a frequency range associated with the resonancefrequency fc, whereby the power factor of the power supply apparatus isimproved.

Patent Documents 1 to 3 are examples of the prior techniques forimproving the power factor of the power supply apparatus that appliesalternating-current electric power to the plasma generator being thecapacitive load.

The power supply apparatus for alternating-current load disclosed inPatent Document 1 includes a transformer (inductor) for improving thepower factor which is provided for a discharge load (discharge cell)that generates plasma.

The power supply apparatus for alternating-current load disclosed inPatent Document 2 includes a transformer (inductor) for improving thepower factor which is provided for a discharge load (discharge cells)that generates plasma. Patent Document 2 discloses that the invertercircuit unit having the frequency control function allows for the powerfactor in the inverter output unit to be optimally controlled in theregion in which greater electric power is input to the load. The powersupply apparatus according to Patent Document 2 performs the frequencycontrol to allow proper operation, during the occurrence of failure inone or some of the discharge cells, through the use of the remainingdischarge cells.

According to the technique in Patent Document 3, in the plasma generatorincluding a plurality of discharge cells, load de-energization fuses areprovided for the respective discharge cells. According to the techniquein Patent Document 3, any failure in a discharge cell causes a fuseprovided correspondently to the discharge cell to burn out, thusinterrupting the electric power supplied to the discharge cell. Further,Patent Document 3 discloses the power supply apparatus for three-phasealternating-current loads and the system for improving the power factorby operating the power supply apparatus at a predetermined frequencyaround the resonance through the use of the load capacitance value andreactors, the predetermined frequency being fixed on the power supplyapparatus side.

The respective power supply apparatuses according to the above-mentionedpatent documents include, for the improvement of power factor, inductiveinductances (reactors) each located between the output side of the powersupply apparatus and the plasma generator.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent No. 3719352

Patent Document 2: Japanese Patent No. 4108108

Patent Document 3: Japanese Patent Application Laid-Open No. 10-25104(1998)

SUMMARY OF INVENTION Problems to be Solved by the Invention

In supplying electric power to the plasma generator, it is important toensure the stable supply of the electric power to the plasma generator.This is because the failure to stably supply the electric power wouldcause variations in, for example, the concentration of the gas generatedin the plasma generator. For the stable supply of electric power, it isimportant to keep and control the amount of electric power input fromthe power supply apparatus to be constant with a high accuracy.

The conventional power supply apparatus for the capacitive load has usedthe load current or the inverter output current as the means forcontrolling the electricity amount of the load. If the load power factorvaries depending on the load conditions, the phase of the current andthe phase of the voltage associated with the inverter output and theload output change accordingly all the time, failing to provideproportional one-to-one correspondence for the detected load current orfor the amount of electric power input to the load. It is thereforedifficult to perform the feedback control on a proportional basis overthe amount of electric power input to the load, and thus the electricpower input has been variably controlled indirectly through the relativefeedback control. In terms of the long-term stable operation of theplasma generator, the disturbance in the load and changes in theexternal setting conditions would be accompanied by changes in theplasma load conditions, and thus the constant electric power inputsupplied from the power supply apparatus would not be secured, failingto provide more reliable control over the apparatus.

The present invention therefore has an object to provide a power supplyapparatus capable of keeping the amount of electric power input constantand stably supplying an plasma generator with the amount of electricpower input in a system including the plasma generator and the powersupply apparatus.

Means to Solve the Problems

To achieve the above-mentioned objective, a power supply apparatusaccording to the present invention is a power supply apparatus thatoutputs an alternating-current voltage to a plasma generator being acapacitive load including a plurality of discharge cells connected toone another. The power supply apparatus includes an inverter thatconverts direct-current electric power to alternating-current electricpower, a controller that controls an action of the inverter, and adetection unit that detects direct-current electric power input to theinverter. The controller (A) determines a target direct-current electricamount value in accordance with an external input, and (B) performsfeedback control on the basis of at least a direct current detected bythe detection unit in such a manner that an amount of the direct-currentelectric power input to the inverter reaches the target direct-currentelectric amount value.

Effects of the Invention

The power supply apparatus according to the present invention is thepower supply apparatus that outputs an alternating-current voltage tothe plasma generator being the capacitive load including the pluralityof discharge cells connected to one another. The power supply apparatusincludes the inverter that converts direct-current electric power toalternating-current electric power, the controller that controls anaction of the inverter, and the detection unit that detectsdirect-current electric power input to the inverter. The controller (A)determines the target direct-current electric amount value in accordancewith the external input, and (B) performs the feedback control on thebasis of at least a direct current detected by the detection unit insuch a manner that the amount of the direct-current electric power inputto the inverter reaches the target direct-current electric amount value.

Thus, the above-mentioned power supply apparatus performs the feedbackcontrol through the use of, for example, the direct current that issmaller than the load current or the like, and the direct current or thelike and the amount of the direct-current electric power input to theinverter (in other words, the amount of electric power input) are inone-to-one correspondence. Thus, the power supply apparatus can control,with a high accuracy, the amount of electric power input to be constantat the target electric input amount value in accordance with the desiredgas concentration. Unlike the load current and the like, the detecteddirect current and the like do not carry, for example, noises. Again,the amount of electric power input is thus controlled, with a highaccuracy, to be constant at the target electric input amount value inaccordance with the desired gas concentration. Thus, the power supplyapparatus can continue to supply the plasma generator with the stableelectric power.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A block diagram showing an inner structure of a power supplyapparatus (10) according to the present invention and a plasma generator(5) connected to the power supply apparatus (10).

FIG. 2 A characteristic diagram for describing an action of the powersupply apparatus (10) according to an embodiment 1.

FIG. 3 A characteristic diagram for describing the action of the powersupply apparatus (10) according to the embodiment 1.

FIG. 4 A diagram showing signals input to an inverter (3) and waveformsoutput from the inverter (3).

FIG. 5 A distributed equivalent circuit diagram showing the state ofdischarge cells connected in parallel in the plasma generator (5).

FIG. 6 A diagram showing an equivalent circuit obtained by combining thedischarge cells connected in parallel in the plasma generator (5).

FIG. 7 A characteristic diagram for describing the power supplyapparatus (10) according to an embodiment 2.

FIG. 8 A current-voltage vector diagram for describing the power supplyapparatus (10) according to the embodiment 2.

FIG. 9 A diagram showing a circuit for describing the power supplyapparatus (10) according to the embodiment 2.

FIG. 10 A current-voltage vector diagram for describing the power supplyapparatus (10) according to the embodiment 2.

FIG. 11 A diagram showing a circuit for describing the power supplyapparatus (10) according to the embodiment 2.

FIG. 12 A current-voltage vector diagram for describing the power supplyapparatus (10) according to the embodiment 2.

FIG. 13 A diagram showing a transformer equivalent circuit fordescribing the power supply apparatus (10) according to the embodiment2.

FIG. 14 A characteristic diagram for describing the power supplyapparatus (10) according to an embodiment 4.

FIG. 15 A diagram showing the state in which a plurality of transformers(4) are connected in parallel.

FIG. 16 A diagram showing characteristics of an inverter output powerfactor η relative to an inverter frequency f.

FIG. 17 A diagram showing characteristics of the inverter output powerfactor η relative to the inverter frequency f.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a power supply apparatus that outputsan alternating-current voltage to a plasma generator being a capacitiveload. The plasma generator includes a plurality of discharge cellsconnected to one another and is capable of generating an ozone gas and aradical gas at high purities and high concentrations. The capacitivepower factor (load power factor) of the plasma generator is, forexample, equal to or less than 50%. The output of each power supplyapparatus under study falls within the range of, for example, 1 kW to100 kW. The plasma generator under study works by the power supply fromthe power supply apparatus that provides an alternating-current outputat a frequency in 10- to 60-kHz range.

FIG. 1 is a block diagram showing a configuration of a system includingthe power supply apparatus and the plasma generator being a capacitiveload.

With reference to FIG. 1, a plasma generator 5 is a capacitive loadincluding a plurality of discharge cells connected in parallel. Asdescribed above, each discharge cell includes a pair of electrodesopposed to each other so as to form a discharge space therebetween. Theelectrodes are provided with a dielectric facing the discharge space.Typical examples of the plasma generator 5 include an ozone gasgenerator (ozonizer). In general, such an ozone generator has beenmainly used in the industrial and manufacturing fields for the ozonesterilization in the field of water treatment and for the ozonebreaching in chemical plants.

The plasma generator 5 is supplied with a source gas such as an oxygengas. The flow rate of the source gas is controlled by a simplecombination of a gas flowmeter and a gas flow valve. The gas pressure inthe plasma generator 5 is adjusted through the use of an output gasvalve of a gas outlet of the plasma generator 5. A refrigerant such aswater is caused to flow in the plasma generator 5 to remove the heatgenerated in the discharge cells, thereby cooling the discharge cells.The flow rate of the refrigerant is adjusted by, for example, awater-cooled valve.

As described above, the gas flow rate, the gas pressure, the refrigerantflow rate, and the like are adjusted by, for example, simple valves, andaccordingly may vary greatly relative to the set values of the gas flowrate, the gas pressure, and the refrigerant flow rate. As will bedescribed below, it is important to regulate such variations in thephysical quantities and to control and keep the physical quantitieswithin predetermined values such that the plasma generator 5 cancontinue to operate stably.

As shown in FIG. 1, the plasma generator 5 is connected with a powersupply apparatus 10 according to the present invention. The power supplyapparatus 10 applies a high voltage alternating current being, forexample, equal to or greater than 1000V to each discharge cell in theplasma generator 5. The application of voltage between the electrodes ofthe discharge cell through the dielectric and the discharge space causesa high-field discharge in the discharge space. This discharge excitesthe source gas supplied in the discharge space. Then, a plasmaphotochemical reaction occurs to generate a plasma gas, such as an ozonegas and a radical gas, from the source gas.

The power supply apparatus 10 is capable of outputting, to the plasmagenerator 5, a variable alternating current which ranges, for example,from 0 to 4000 W.

The following specifically describes the power supply apparatus 10according to the present invention with reference to the drawingsdescribing embodiments of the invention.

Embodiment 1

With a view toward protecting the load against a short circuit, thepower supply apparatus 10 according to the present embodiment includes,in place of fuses for the respective discharge cells, a protectioncoordination function that protects the load against a short circuitoccurring downstream from the inverter output unit. The power supplyapparatus 10 is configured to interrupt the inverter output voltage in avery short period of time when any abnormality is encountered. Thus, thepower supply apparatus 10 according to the present embodiment is readyto manage failures. Further, the power supply apparatus 10 according tothe present embodiment indicates a faulty part in the event of afailure. This indication helps the user to restore the malfunctioningpower supply apparatus 10 in a short period of time.

As shown in FIG. 1, the power supply apparatus 10 includes adirect-current voltage output unit 20, an inverter 3, and a transformer4.

The direct-current voltage output unit 20 may be a direct-currentconverter that converts commercial alternating-current electric powersupply into a direct-current voltage and outputs the direct-currentvoltage or may be a direct-current battery that outputs the accumulateddirect-current voltage. The direct-current converter receives an inputof single-phase or three-phase commercial alternating-current electricpower supply (for example, 200V) from the outside, rectifies thealternating-current voltage, coverts the voltage into a direct-currentvoltage, and outputs the boosted direct-current voltage. Thedirect-current battery boosts the direct-current voltage output formbattery cells in multistage connection up to a predetermineddirect-current voltage, and then outputs the boosted direct-currentvoltage.

The direct-current voltage output unit 20 is connected with the inverter3 located downstream therefrom. The direct-current voltage output fromthe direct-current voltage output unit 20 is converted into ahigh-frequency alternating-current voltage in the inverter 3, and thenthe inverter 3 outputs the high-frequency alternating-current voltage.

The inverter 3 is connected with the transformer 4 located downstreamtherefrom. The transformer 4 boosts the high-frequencyalternating-current voltage output from the inverter 3 up to a voltagethat can induce discharge in the plasma generator 5. The transformer 4is connected with the plasma generator 5 located downstream from thetransformer 4. The transformer 4 applies the boosted high-frequencyalternating-current voltage to the plasma generator 5 being a capacitiveload.

Provided in the power supply apparatus 10 is a controller 6 thatcontrols the action of the inverter 3. Through the control by thecontroller 6, the system shown in FIG. 1 can be driven stably, promptlystop operating in the event of a failure, and promptly handle thefailure, allowing the power supply apparatus 10 to operate stably for along period of time.

Provided between inverter 3 and the transformer 4 in the power supplyapparatus 10 is a current-limiting reactor Lc that regulates ashort-circuit current. The current-limiting reactor Lc provides theprotection coordination in the power supply apparatus 10 in the event ofa short circuit occurring in a load located downstream from the outputunit of the inverter 3, prevents damages on the switchboard and the likelocated outside the power supply apparatus 10, and prevents failures ofmain components of the power supply apparatus 10, and accordingly thepower supply apparatus 10 can promptly shut off the power supply.

In the conventional plasma generator, an inductive load locatedimmediately downstream from the inverter output of the power supplyapparatus for alternating-current load is capacitive, and thus the maincomponents of the power supply apparatus as well as the discharge cellsmay be broken. Such a breakage is mainly caused by a flow of greatinrush current (load capacitor current), the concentration of dischargein a part of the discharge cell surface, and the abnormal dischargeoccurring outside the discharge cell portion. Thus, according to thetechnique in Patent Document 3, each discharge cell is provided with aprotective fuse. According to the present invention, instead of theprotective fuse, the current-limiting reactor Lc for current regulationis disposed on the output side of the inverter 3. Further, the pulsewidth of the inverter 3 is controlled, and accordingly the load currentand the load voltage are managed to prevent the concentration ofdischarge in a part of the discharge cell surface. The output of thepower supply apparatus is accordingly controlled to regulate ashort-circuit current in the event of a short circuit in the load andsupply a stable alternating-current voltage to the load side for a longperiod of time.

Provided on the output side of the inverter 3 of the power supplyapparatus 10 are detection units 31, 32, 41, and 42. The detection units31 and 32 are disposed between the inverter 3 and the transformer 4. Thedetection unit 31 detects an output current Io from the inverter 3 andthe detection unit 32 detects an output voltage Vo from the inverter 3.The detection units 41 and 42 are disposed between the transformer 4 andthe plasma generator 5. The detection unit 41 detects the load currentId output from the transformer 4 and the detection unit 42 detects theload voltage Vd output from the transformer 4.

The detection units 31, 32, 41, and 42 continuously perform thedetection action and transmit the detection results as signals to thecontroller 6. The controller 6 causes the inverter 3 to stop in responseto the detection of any short circuit by the detection units 31, 32, 41,and 42. That is, the controller 6 determines the presence of shortcircuit on the basis of the detection results transmitted from thedetection units 31, 32, 41, and 42. If the presence of short circuit isdetected, the controller 6 sends a gate shut-off signal to an inverterdrive circuit 62 through a logic circuit 61. Consequently, the outputfrom the inverter 3 can be stopped. The controller 6 transmits to thelogic circuit 61, a drive signal (f: drive pulse cycle of the inverter3=1/f, τ: (output) pulse width of the inverter 3).

Thus, in the event of a short circuit in the load, the output from theinverter 3 is stopped in about microseconds. Further, the controller 6indicates (makes a notification of) an abnormal spot causing a shortcircuit, thus enhancing the stable stopping function performance of thepower supply apparatus for alternating-current load.

Specifically, the load voltage Vd of the plasma generator 5 duringnormal operation usually has the characteristics that are dependent onthe load current Id shown in FIG. 2. That is, the load voltage Vd isexpressed by Vd=f(Id) (the solid line in FIG. 2) and the plasmagenerator 5 is driven while keeping the load voltage Vd. In the event ofan abnormality in the plasma generator 5, however, the plasma generator5 fails to keep operating at the load voltage Vd, and accordingly anextremely low voltage is detected.

Thus, an approximate predetermined voltage Vth is set for the controller6, the approximate predetermined voltage Vth being equal to or smallerthan, for example, about 0.3 times the load voltage Vd and beingexpressed by Vth=c×Id+d (c, d: constants, the alternate short and dashedlines in FIG. 2). Here, provided between the transformer 4 and theplasma generator 5 are the current detector 41 and the voltage detector42. The detectors 41 and 42 continuously detect the current value andthe voltage value supplied to the plasma generator 5.

Assume that the current detector 41 detects a current value Id1 and V1denotes a voltage detection value detected by the voltage detector 42when the current value Id1 is detected. Then, assume that the controller6 receives the respective detection values Id1 and V1 and determinesthat the voltage detection value V1 is equal to or smaller than thepredetermined voltage Vth (=c×Id1+d).

In this case, the controller 6 determines the occurrence ofabnormalities in the plasma generator 5 (the occurrence of short circuiton the input side of the plasma generator 5), and accordingly thecontroller 6 transmits a gate shut-off signal for stopping the outputfrom the inverter 3. The logic circuit 61 receives the above-mentioneddrive signal (f, τ) and the gate shut-off signal, and then outputs, tothe inverter drive circuit 62, the gate shut-off signal being the logicresult. Then, the output from the inverter 3 is stopped on the basis ofthe gate shut-off signal. In the above-mentioned case, the controller 6causes a display apparatus (not shown) to display the abnormalities tonotify the occurrence of abnormalities in the plasma generator 5, sothat the user is notified of the abnormalities.

Meanwhile, the voltage Vo output from the inverter 3 is the voltage onthe primary side of the high-voltage transformer 4, and monitoring thevoltage Vo allows the detection of abnormal conditions in the outputload portion including the transformer 4.

The characteristics of the inverter output voltage Vo under the normalconditions are usually dependent on the inverter output current Io shownin FIG. 3. That is, the inverter output voltage Vo is expressed by Vo=f(Io) (the solid line in FIG. 2) and the power supply apparatus 10 isdrive while keeping the inverter output voltage Vo. In the event ofabnormalities in the plasma generator 5 or the transformer 4, however,power supply apparatus 10 fails to keep the inverter output voltage Vd,and accordingly an extremely low voltage is detected.

Thus, an approximate predetermined voltage V′th is set for thecontroller 6, the approximate predetermined voltage V′th being equal toor smaller than, for example, about 0.3 times the inverter outputvoltage Vo and being expressed by V′th=a×Io+b (a, b: constants, thealternate short and dashed lines in FIG. 3). Here, provided between theinverter 3 and the transformer 4 are the current detector 31 and thevoltage detector 32. The detectors 31 and 32 continuously detect thecurrent value and the voltage value output from the inverter 3.

Assume that the current detector 31 detects a current value Io2 and V2denotes a voltage detection value detected by the voltage detector 32when the current value Io2 is detected. Then, assume that the controller6 receives the respective detection values Io2 and V2 and determinesthat the voltage detection value V2 is equal to or smaller than thepredetermined voltage V′th (=a×lo+b).

In this case, the controller 6 determines the occurrence ofabnormalities in the transformer 4 and/or in the plasma generator 5 (theoccurrence of short circuit on the output side of the inverter 3), andaccordingly the controller 6 transmits a gate shut-off signal forstopping the output from the inverter 3. The logic circuit 61 receivesthe above-mentioned drive signal (f, τ) and the gate shut-off signal,and then outputs, to the inverter drive circuit 62, the gate shut-offsignal being the logic result. Then, the output from the inverter 3 isstopped on the basis of the gate shut-off signal. In the above-mentionedcase, the controller 6 further causes the display apparatus (not shown)to display the abnormalities to notify the occurrence of abnormalitieson the output side of the inverter 3, so that the user is notified ofthe abnormalities.

As described above, the power supply apparatus 10 includes thecurrent-limiting reactor Lc provided at the output unit of the inverter3, and accordingly any failure (short circuit) can be handled (ashort-circuit current can be regulated). The current-limiting reactor Lcwith an inductance of about 20 μH to several hundred μH can regulate anextremely great short-circuit current in the event of a short circuitoccurring downstream from the output unit of the inverter 3. Thus, thecurrent-limiting reactor Lc not only prevents failures of the powersupply apparatus 10 but also allows the power supply apparatus 10 toserve as a safe power supply that provides the protection coordination.

If the power supply apparatus 10 provides insufficient protectioncoordination, any failure such as a short circuit in the system shown inFIG. 1 can turn off the breaker of the switchboard for the entirefactory in which the system is installed. According to the presentinvention, meanwhile, the power supply apparatus 10 includes thecurrent-limiting reactor Lc mentioned above, and accordingly such anoutcome can be avoided.

The electric capacitance of the current-limiting reactor Lc increaseswith the square of the output current value of the inverter 3(=2·π·f·L·I²). In a case where the load is capacitive, the voltageapplied to the current-limiting reactor Lc is boosted relative to theoutput voltage of the inverter 3. Thus, the electric capacitance of thecurrent-limiting reactor Lc increases greatly as a reactor value L ofthe current-limiting reactor Lc increases, resulting in an expansion theentire outline of the power supply apparatus 10 and an increase in theweight of the power supply apparatus 10. With a view toward reducing thesize and the weight of the power supply apparatus 10 according to thepresent invention that supplies power to the plasma generator 5including a plurality of discharge cells, the reactor value L of thecurrent-limiting reactor Lc disposed in power supply apparatus 10, inparticular, is preferably set within the range of about 20 μH to 70 μH.

The power supply apparatus 10 has the function of stopping the outputfrom the inverter 3 by making quick decisions in the event of a shortcircuit, thus allowing for a quick recovery. That is, the power supplyapparatus 10 stops supplying power and makes a notification of the spotin which the abnormality has occurred, whereby the power supply can bepromptly resumed.

Meanwhile, the load conditions of the plasma generator 5 variesdepending on the electric power supplied to the plasma generator 5, thesupplied gas flow rate of the source gas, the gas pressure in the plasmagenerator 5, and the temperatures of the discharge cells. The controldescribed below is therefore important for the stable generation of thedesired amount of ozone and the like in the desired concentrations bythe plasma generator 5 through the use of plasma. That is, the plasmagenerator 5 is controlled from the power supply apparatus side toregulate, within a given accuracy range, the supplied gas flow rate of asource gas 70 supplied to the respective discharge cells, the gaspressure in the plasma generator 5, the flow rate of a refrigerant 78supplied and circulated in the plasma generator 5 to cool the dischargecells, the temperature associated with the refrigerant, and theconcentration of a gas 76 output from the plasma generator 5. Thiscontrol allows the plasma state generated in the plasma generator 5 towork in the stable region, and accordingly allows the plasma generator 5to operate stably.

Provided on the plasma generator 5 side are a gas flow rate adjuster 71capable of measuring and adjusting the supplied gas flow rate of thesource gas 70, a gas pressure adjuster 73 capable of measuring andadjusting the gas pressure in the discharge cells, a refrigeranttemperature adjuster 74 capable of measuring and adjusting thetemperature of the refrigerant 78 supplied and circulated in the plasmagenerator 5, a refrigerant flow rate adjuster 75 capable of measuringand adjusting the flow rate of the refrigerant, and a concentrationdetector (monitor) 72 capable of measuring the concentration of the gas76 generated in plasma generator 5 (see FIG. 1).

The gas flow rate adjuster 71 adjusts the supplied gas flow rate of thesource gas with an accuracy of, for example, ±5% (within a desiredrange) relative to the set gas flow rate. The gas pressure adjuster 73adjusts the gas pressure in the discharge cells with an accuracy of, forexample, ±5% (within a desired range) relative to the set gas pressure.The refrigerant temperature adjuster 74 adjusts the temperature of therefrigerant with an accuracy of, for example, ±10% (within a desiredrange) relative to the set refrigerant temperature. The refrigerant flowrate adjuster 75 adjusts the circulation flow rate of the refrigerantwith an accuracy of, for example, ±10% (within a desired range). Theconcentration of the gas 76 generated in the plasma generator 5 ismeasured with an accuracy of, for example, ±2% (within a desired range).The respective items are controlled and managed within theabove-mentioned ranges through the transmission and receipt of signalsbetween the plasma generator 5 and the power supply apparatus 10, andaccordingly the desired amount of the gas 76 in the desired gasconcentration is output from the plasma generator 5.

The controller 6 transmits and receives, through an external signalinterface 63 of the power supply apparatus 10 whenever necessary, theset value of the supplied gas flow rate set for the gas flow rateadjuster 71, the value of the supplied gas flow rate measured by the gasflow rate adjuster 71, the set value of the gas pressure set for the gaspressure adjuster 73, the value of the gas pressure measured by the gaspressure adjuster 73, the refrigerant temperature measured by therefrigerant temperature adjuster 74, the set value of the refrigerantflow rate set for the refrigerant flow rate adjuster 75, and the valueof the refrigerant flow rate measured by the refrigerant flow rateadjuster 75. The amount of electric power output from the power supplyapparatus 10 to the plasma generator 5 is controlled and managed throughthe transmission and receipt of the values. The plasma generator 5accordingly generates and outputs the gas 76 with the stable flow rateand the stable concentration, and the above-mentioned physicalquantities in the plasma generator 5 are monitored.

Here, the gas flow rate adjuster 71 and the refrigerant flow rateadjuster 75 may be, for example, mass flow controllers (MFCs) thatcontrol the gas flow rate with a high degree of accuracy. The gaspressure adjuster 73 may be, for example, an automatic pressurecontroller (APC) that controls the gas pressure to be constant all thetime.

Further, provided on the plasma generator 5 side is the gas detector 72that detects the gas concentration of the generated ozone gas and theflow rate of the ozone gas (see FIG. 1). The gas concentration and thegas flow rate detected by the gas detector 72 are also transmitted tothe controller 6 through the external signal interface 63 whenevernecessary.

According to the present embodiment, the controller 6 transmits andreceives the supplied gas flow rate of the source gas (the set valuesignal and the detection value associated with the gas flow rateadjuster 71) and determines if the supplied gas flow rate falls withinthe above-mentioned desired range relative to the set gas flow ratewhile the power supply apparatus 10 controls the pulse width or thepulse frequency of the inverter 3 so as to output the electric power inaccordance with the flow rate of the flowing gas and the concentrationof the generated gas 76. The controller 6 determines whether thepressure in the discharge cells (the set value signal and the detectionvalue associated with the gas pressure adjuster 73) falls within theabove-mentioned desired range relative to the set gas pressure. Thecontroller 6 determines whether the temperature of the refrigerant (thedetection value associated with the refrigerant temperature adjuster 74)falls within the above-mentioned desired range relative to the setrefrigerant temperature. The controller 6 determines whether the flowrate of the refrigerant (the set value signal and the detection valueassociated with the refrigerant flow rate adjuster 75) falls within theabove-mentioned range relative to the set refrigerant flow rate). If thedetection signals (detection values) are out of the respective desiredranges, the power supply apparatus 10 issues an abnormality signal toimmediately stop the plasma generator 5 or performs, for example, thecontrol over the pulse width of the inverter 3 to control the outputelectric power. This allows the monitoring for the stable operation ofthe plasma generator 5 such that the concentration of the generated gasdoes not fall outside the desired range.

For the above-mentioned determination, the following assumptions aremade: the controller 6 detects that the supplied gas flow rate of thesource gas (the detection value associated with the gas flow rateadjuster 71) falls outside the desired range relative to the set gasflow rate; the controller 6 detects that the pressure in the dischargecells (the detection value associated with the gas pressure adjuster 73)falls outside the desired range relative to the set gas pressure; thecontroller 6 detects that the temperature of the refrigerant (thedetection value associated with the refrigerant temperature adjuster 74)falls outside the desire range relative to the set refrigeranttemperature; or the controller 6 detects that the flow rate of therefrigerant (the detection value associated with the refrigerant flowrate adjuster 75) falls outside the desired range relative to the setrefrigerant flow rate.

In the respective cases, the controller 6 sends a gate shut-off signal602 to the inverter drive circuit 62 through the logic circuit 61.Consequently, the output from the inverter 3 is immediately stopped.Here, the logic circuit 61 receives, from the controller 6, a drivesignal (f: drive pulse cycle of the inverter 3=1/f, τ: pulse width ofthe inverter 3) 601.

Thus, in response to any abnormal physical quantity encountered in theplasma generator 5, the output from the inverter 3 is stopped in aboutmicroseconds. Further, the controller 6 causes the display apparatus(not shown) to display (notify) the occurrence of abnormality (which oneof the physical quantities is abnormal) in the plasma generator 5. Thus,the user can immediately recognize that the above-mentioned physicalquantity in the plasma generator 5 is abnormal.

In the present embodiment, the environmental conditions for theoperation of the plasma generator 5 are kept constant. Further, thepower supply apparatus 10 adjusts the inverter 3 such that the powersupply apparatus 10 can output the optimal amount of electric power inaccordance with the physical quantities, such as the flow rate, thepressure, the temperature, and the like in the plasma generator 5 andimmediately detects any abnormal physical quantities. In the event ofabnormalities, the power supply apparatus 10 can stop the output fromthe inverter 3. In the event of abnormalities associated with thephysical quantities, the power supply apparatus 10 makes a notificationof the abnormalities, and accordingly the user can immediately recognizethe abnormalities in the plasma generator 5. The abnormal conditionsthat can cause a short circuit in the load of the plasma generator 5,such as a sudden falloff in the gas flow rate, a sudden falloff in thepressure in the discharge cells, a reduction in the amount of coolingwater, an increase in the temperature of the cooling water, aremonitored on the power supply apparatus 10 side. Thus, factorsresponsible for instabilities in the plasma generator 5 can be found inadvance, and accordingly the power supply apparatus 10 is controlled toavoid abnormalities associated with a short circuit in the load andabnormal conditions associated with overvoltage.

With reference to FIG. 4, the following describes the outputting of adrive signal 601 and the gate shut-off signal 602 from the controller 6to the logic circuit 61 and how the waveforms output from the inverter 3change in accordance with the outputting. The ON-OFF signals for twogate signals are respectively shown in the second and third columns inFIG. 4. The two signals are combined to provide one drive signal 601.

The controller 6 transmits, to the logic circuit 61, the drive signal(the gate signals, ON-OFF signals) 601 that directly drives the inverter3. The drive signal is shown in the second and third column in FIG. 4.The logic circuit 61 provides, on the basis of the drive signal, thedrive pulse cycle (1/f) and the pulse width τ of the inverter 3 asinstructions to the inverter drive circuit 62 that drives the inverter3. The inverter drive circuit 62 that have received the instructionsdrives the inverter 3 in accordance with the drive pulse cycle (1/f) andthe pulse width τ (see the first column (the top column) in FIG. 4).

The above-mentioned action is performed while the gate shut-off signal(the bottom column in FIG. 4) 602 is the H signal (normal). In a casewhere the gate shut-off signal 602 is the L signal (in the event of anabnormality), the logic circuit 61 transmits, to the inverter drivecircuit 62, the instructions to stop the inverter 3 regardless of theinputting of the drive signal. The inverter drive circuit 62 that havereceived the instructions stops the output from the inverter 3. Asdescribed above, the output from the inverter 3 can be stopped in aboutmicroseconds if the gate shut-off signal 602 is the L signal.

Normally, the waveforms associated with the drive pulse cycle (1/f) andthe pulse width τ are output from the inverter 3, and then the powersupply apparatus 10 supplies high-frequency and high-voltage electricpower to the plasma generator 5 on the basis of the waveforms. Thesupplied gas flow rate, the gas pressure, the refrigerant flow rate, andthe refrigerant temperature in the plasma generator 5 fall within thedesired ranges, thus allowing for the stable operation of the plasmagenerator 5.

The transmission and receipt of the setting signals and the detectionsignal values associated with the supplied gas flow rate, the gaspressure, the refrigerant flow rate, the refrigerant temperature, andthe like are performed between the plasma generator 5 and the powersupply apparatus 10. This allows for the stable operation of the plasmagenerator 5. Thus, to supply the optimal electric power to plasmagenerator 5, the power supply apparatus 10 performs the feedforwardcontrol and the feedback control over the pulse width and the pulsefrequency of the inverter 3 in accordance with the setting signals andthe detection signal values.

Embodiment 2

As described below, the power supply apparatus 10 according to thepresent embodiment has a configuration that is based on the parallelresonance and highly resistant to load variations.

For the capacitive load such as the plasma generator 5, the phase of thecurrent is approximately 90° leading relative to the phase of thevoltage waveform. Although the electric capacitance supplied to theplasma generator 5 is extremely great, the stable inputting of energy tothe plasma generator 5 can be achieved only if the active power is inthe range of about ⅕ to 1/10 of the electric capacitance (the load powerfactor is in the range of about 10% to 20%). Therefore, the power supplyapparatus 10 has been in need of an extremely large electric capacity.Here, the inductive reactor is disposed for the power factor improvementassociated with the load power factor of the power supply apparatus 10(to create the resonance state between the plasma generator 5 and thepower supply apparatus 10).

In the present embodiment, the transformer 4 in the power supplyapparatus 10 described in an embodiment 1 is a high-performancetransformer that has the secondary-side magnetizing inductance more thanfive times as great as the leakage inductance. The inductance value isobtained by substituting the capacitance value and the working frequencyof the plasma generator 5 into Expression (1) such that the resonancefrequency (see Expression (1)) falls within the operating frequencyrange of the plasma generator 5. The calculated inductance value isgiven as the inductance value (hereinafter referred to as a transformerinductance value) obtained by combining the secondary-side magnetizinginductance and the leakage inductance of the transformer 4. Thus, thetransformer 4 according to the present embodiment serves as thehigh-performance transformer that has the function of resonating withthe load as well as the conventional functions including the voltageboosting function and insulating function and is dedicated to the plasmagenerator 5. The present embodiment is described below in detail.

FIG. 5 is an equivalent circuit diagram showing a plurality of dischargecells connected in parallel in the plasma generator 5. FIG. 6 is anequivalent circuit diagram obtained by combining the plurality ofdischarge cells shown in FIG. 5. Assuming that the power supplyapparatus 10 applies a load voltage Vd0 to the plasma generator 5including the equivalent circuit shown in FIG. 6 and causes a loadcurrent Id0 to flow through the plasma generator 5, the actual currentflowing through the respective discharge cells vary for the followingreasons.

Assuming that the plurality of discharge cells are connected in parallelas illustrated in FIG. 5, wire inductance LN formed of a wire is presentin the length portion of the wire. When the load voltage Vd0 is appliedto the plasma generator 5, the voltage applied to the respectivedischarge cells varies due to the voltage reduction effect (or voltageboosting effect) caused by the current flowing through the wire and thewire inductance LN. Consequently, the current flows unevenly though therespective discharge cells. In a case where the plurality of dischargecells are connected in parallel, the variations in the electric power(current) input to the respective discharge cells become greater.

The relationship among the respective current values Id0, Id1, Id2, . .. , and Idn shown in FIG. 5 is expressed as Id0/n (n: the number ofdischarge cells)≠Id1≠Id2 . . . ≠Idn.

Further, the range of variation in the discharge cell current (Id1, Id2,. . . , and Idn) flowing through each discharge cell in theabove-mentioned expression is greatly dependent on variations in, forexample, the manufacturing accuracy and the setting conditions (such asthe set value for the supplied gas flow rate of the source gas, the setvalue for the gas pressure in the discharge cell, the set value for thesupplied amount of refrigerant, the set value for the temperature of therefrigerant, and the like) for each cell. In the plasma generatorincluding the plurality of discharge cells connected in parallel, thedischarge cell current flowing through each discharge cell greatlyvaries due to the wire inductance LN besides the manufacturing accuracyand the setting conditions for each discharge cell.

Assuming that the load voltage Vd0 is applied to the equivalent circuitshown in FIG. 6 (plasma generator 5), plasma load power Pw input to theplasma generator 5 is given by the following expression including therespective constants of the discharge cells but excluding the wireinductance LN.Pw=α·V*·Ib0=4·Cg0·V*·f·{2^(0.5)·Vd0−(1+Ca0/Cg0)·V*}=[A·F(Vd0)+B]·f  Expression (2)

Here, the plasma discharge conduction ratio (<1.0) in the dischargespace is denoted by a. The self-sustaining discharge voltage is denotedby V*. As shown in FIG. 6, the total discharge plasma current is denotedby Ib0. As shown in FIG. 6, the dielectric capacitance value obtained bycombining the capacitance values of the dielectric portions in therespective discharge cells is denoted by Cg0. The working frequency(kHz) of the high-frequency alternating-current voltage applied to theplasma generator 5 is denoted by f. As shown in FIG. 6, the dischargespace capacitance value obtained by combining the capacitance values ofthe discharge space portions in the respective discharge cells isdenoted by Ca0. It is indicated by F(Vd0) that the value is the functiondependent on the load voltage Vd0 applied between the discharge cells. Aand B are constants determined by the plasma generator 5.

With the above-mentioned constants A and B and the frequency f beingprovided, the plasma load power Pw is uniquely given correspondently tothe plasma load voltage Vd0 (kV) applied to the discharge cells. Asshown in FIG. 7, the plasma load power Pw (W) has a characteristic ofincreasing linearly along with the plasma load voltage Vd0 (kV)according to the above-mentioned expression given for Pw.

With reference to FIG. 7, the vertical axis on the left indicates theplasma load power Pw (W), the vertical axis on the right indicates theinverter output (%) of the inverter 3 included in the power supplyapparatus 10 that provides power supply to the plasma generator 5, andthe horizontal axis indicates the plasma load voltage Vd0 (kV). Withreference to FIG. 7, it is assumed that the frequency f is fixed to 15.5kHz for a characteristic 2003, the frequency f is fixed to 16.0 kHz fora characteristic 2004, and the frequency f is fixed to 16.5 kHz for acharacteristic 2005.

Next, FIG. 8 is obtained by examining the phase vector of the plasmaload voltage Vd0 applied to the plasma generator 5 and the phase vectorof the total load current Id0 flowing through the plasma generator 5shown in FIG. 6. The phase vector in FIG. 8 expresses, in the vectorform, the voltage phase and the current phase applied to the respectiveportions of the discharge cells with reference to the phase vector forthe self-sustaining discharge voltage V* applied to the discharge spacein the equivalent circuit and the current (discharge current) Ib0flowing through the discharge space.

With reference to FIG. 8, in the discharge space shown in the equivalentcircuit in FIG. 6, an electric charge Q electrically charged through adielectric capacitor Cg0 is discharged when the electric charge Qexceeds the self-sustaining discharge voltage V* in the discharge space,and then the discharge in the discharge space is immediately stopped inresponse to the discharge of the electric charge Q. Thus, in thedischarge space, the intermittent discharge at the constantself-sustaining discharge voltage V* is repeated in the entire electrodesurface.

The discharge impedance of the discharge portion in the discharge spaceis regarded as a pure resistive load Rp0 (see FIG. 6). Thus, there is nophase difference between the current (discharge current) Ib0 flowingthrough the discharge space and the self-sustaining discharge voltage V*corresponding to the discharge voltage, and accordingly the current Ib0is in phase (zero phase) with the self-sustaining discharge voltage V*.

With reference to the vector diagram in FIG. 8, the state of 0° phase isindicated by the horizontal vector. The vector in which the phase is 90°leading is shown in the upward vertical direction. In contrast, thevector state in which the phase is 90° lagging is defined in thedownward vertical direction.

With reference vector diagram in FIG. 8, assuming that the dischargecurrent Ib0 flows while the phase is at 0° and the applied voltage isα·V*, a total capacitor current Ia0 flows through the space (1−α) inwhich no discharge takes place in the discharge space (through thecapacitance Ca0 in the discharge space). Here, the phase of the totalcapacitor current Ia0 is 90° leading relative to the discharge currentIb0 at the phase zero. Then, as shown in the equivalent circuit in FIG.6, the total load current Id0 is obtained by combining the vector of thedischarge current Ib0 at the zero phase and the vector of the totalcapacitor current Ia0 at the phase that is 90° leading, and thus thetotal load current Id0 at the phase shown in FIG. 8 flows.

Next, the phase of a voltage Vcg applied across the total dielectriccapacitance Cg0 of the dielectric in the discharge cell is defined asthe phase that is 90° lagging relative to the total load current Id0expressed by the vector. Thus, the voltage Vcg at the phase shown inFIG. 8 is applied.

The phase of the total load voltage Vd0 applied to the discharge cell isdefined as the combined vector obtained from the voltage Vcg appliedacross the total capacitance Cg0 of the dielectric and theself-sustaining discharge voltage V* applied across the discharge space.Thus, the total load voltage Vd0 at the phase shown in FIG. 8 isapplied.

It is clear from FIG. 8 that the phase difference of the total loadcurrent Id0 relative to the total load voltage Vd0 applied across thedischarge cells is the leading load that is φ° leading (capacitive). Onthe basis of FIG. 8, the supplied electric power capacity PQ necessaryfor the discharge cells with respect to the discharge power Pw(=α·V*·Ib0) can be obtained by combining the vector of the total loadcurrent Id0 and the vector of the total load voltage Vd0 as in thefollowing expression.PQ=Id0·Vd0 (kVA)

The supplied electric power capacity PQ becomes much greater than thedischarge power Pw.

The load power factor (or the plasma load power factor) rηd (=Pw/PQ×100)in the plasma generator 5 shown in FIG. 6 is the leading load that isleading at a very small percentage around several tens of percent. Thishas required the plasma generator 5 being the capacitive load to have anextremely great output capacity such that the plasma generator 5 cansupply the predetermined discharge power Pw, resulting in the upsizingof the apparatus. The means for solving this problem is the power factorimprovement means for improving the power factor of the load.

The inventors investigated the series-resonance mode power factorimprovement means and the parallel-resonance mode power factorimprovement means to find out the resonance mode that allows the stableoperation of the plasma generator 5 being the capacitive load. That is,the inventors found out the resonance mode that can improve the powerfactor of the plasma generator 5 including a plurality of dischargecells connected in parallel by minimizing variations in the dischargeelectric power amount input into the respective discharge cells. Thiswill be specifically described below.

FIG. 9 is a diagram showing the series-resonance mode power factorimprovement means. With reference to FIG. 9, the plasma generator 5shown in FIG. 6 is connected with the power supply apparatus 10described in the embodiment 1. The power supply apparatus 10 includes aload resonance transformer 7 provided, in series, at the output unit ofthe transformer 4 of the power supply apparatus 10. FIG. 10 is a diagramshowing the vector characteristics associated with the case in which theseries-resonance mode.

FIG. 11 is a diagram illustrating the parallel-resonance mode powerfactor improvement means. With reference to FIG. 11, the plasmagenerator 5 shown in FIG. 6 is connected with the power supply apparatus10 described in the embodiment 1. The power supply apparatus 10 includesthe load resonance transformer 7 provided, in parallel, at the outputunit of the transformer 4 of the power supply apparatus 10. FIG. 12 is adiagram showing the vector characteristics associated with the case inwhich the parallel-resonance mode is employed.

As shown in FIG. 9, the power supply apparatus 10 in theseries-resonance mode includes, as the load resonance transformer 7, areactor Lr provided in series with the transformer 4. As shown in FIG.9, in a case where the load is capacitive and there is a phasedifference between the total load voltage Vd0 and the total load currentId0, a reactive current (reflection current) Ic as well as a current Issupplied from the power supply apparatus 10 flows backward through thetransformer 4 (see the broken line in FIG. 9). Here, the reactivecurrent Ic is the current flowing backward from the plasma generator(load) 5 side to the power supply apparatus 10 side.

The total load current Id0 (=Is+Ic) in which the reactive current Icmerges with the current Is supplied from the power supply apparatus 10to the plasma generator 5 flows through the reactor Lr provided inseries with the load. The total load current Id0 flows through thereactor Lr, thus inducing a reactor voltage VL across the reactor Lr.Naturally, the reactor voltage VL is the voltage that is 90° leadingrelative to the total load current Id0 shown in FIG. 8. That is,deducting the vector voltage of the reactor voltage VL from the vectorvoltage of the total load voltage Vd0 provides a vector voltage Vs,which is a transformer voltage Vs output from the transformer 4.

FIG. 10 is a diagram showing the vector characteristics associated withthe power supply apparatus 10 in the series-resonance mode mentionedabove. That is, the total load current Id0 output from the transformer 4is in phase with the transformer voltage Vs that is the secondaryvoltage of the transformer 4, and accordingly the electric powercapacity (=Id0·Vs) at the output unit of the transformer 4 is improved,approaching the plasma load power Pw (in other words, a power factor 11at the output unit of the transformer 4 is improved, approaching 100%).

In the series-resonance mode, the value of the transformer voltage Vs ismuch smaller than that of the total load voltage Vd0 applied to theload, indicating that the series-resonance mode is the resonance mode inwhich the power supply output is subjected to the voltage amplification.In other words, the transformer voltage Vs is amplified up to the loadvoltage Vd due to the resonance reactor Lr provided in series with thedischarge cell portion. In the series-resonance mode, assuming that theplurality of discharge cells are connected in parallel as shown in FIG.5, the wire inductance LN between the discharge cells serves as a partof the series resonance function. With the plurality of discharge cellsbeing connected in parallel, the voltage amplification degree variesdepending on the magnitude of the wire inductance LN. This causes theload voltage Vd applied across the discharge cells to vary greatly,which may result in a wide range of variation in the amount of electricpower input to the respective discharge cells.

Meanwhile, as shown in FIG. 11, the power supply apparatus 10 in theparallel-resonance mode includes, as the load resonance transformer 7,the reactor Lr provided in parallel with the transformer 4. As shown inFIG. 11, in a case where the load is capacitive and there is a phasedifference between the total load voltage Vd0 and the total load currentId0, the reactive current (reflection current) Ic as well as the currentIs supplied from the power supply apparatus 10 flows backward throughthe resonance reactor Lr (see the broken line in FIG. 11). Here, thereactive current Ic is the current flowing backward from the plasmagenerator (load) 5 side to the power supply apparatus 10 side.

The total load current Id0 (=Is+Ic) in which the reactive current Icmerges with the current Is supplied from the power supply apparatus 10to the plasma generator 5 flows from the power supply apparatus 10 sidetoward the plasma generator 5. In the parallel-resonance mode, only thereactive current Ic flows through the reactor Lr provided in parallelwith the transformer 4. The reactive current Ic flowing through thereactor Lr connected in parallel is the reaction current form the loadside, and thus, the reactive current Ic is the current that is 90°lagging relative to the total load voltage Vd0 applied to the load side.That is, the vector current obtained by combining the total load currentId0 and the reactive current Ic is the current Is output from thetransformer 4.

FIG. 12 is a diagram showing the vector characteristics associated withthe power supply apparatus 10 in the parallel-resonance mode mentionedabove. That is, the total load voltage Vd0 output from the transformer 4is in phase with the current Is that is the output current from thetransformer 4, and accordingly the electric power capacity (=Vd0·Is) atthe output unit of the transformer 4 is improved, approaching the plasmaload power Pw (in other words, the power factor 11 at the output unit ofthe transformer 4 is improved, approaching 100%).

In the parallel-resonance mode, the value of the output current Is fromthe transformer 4 is much smaller than that of the total load currentId0 flowing through the load, indicating that the parallel-resonancemode is the resonance mode in which the power supply output is subjectedto the current amplification.

The inventors conducted the verification test on the series-resonancemode power supply apparatus 10 that supplies power to the plasmagenerator 5 including a plurality of discharge cells connected to oneanother and the parallel-resonance mode power supply apparatus 10 thatsupplies power to the plasma generator 5 including a plurality ofdischarge cells connected to one another, to thereby determine which oneof the power supply apparatuses 10 can drive the plasma generator 5 morestably than the other one.

The results revealed that, with the power being supplied from theseries-resonance mode power supply apparatus 10 to the plasma generator5 mentioned above, the load failed to operate stably or some dischargecells were broken due to the following factors.

That is, as shown in FIG. 5, with the respective discharge cells beingconnected in parallel, the combined impedance and the total dischargeplasma resistance Rp0 of the load decline in inverse proportion to n(the number of discharge cells), the load current increases inproportion to n, and the total load current Id0 varies in a wider range.Further, the wire inductance value LN in the connecting wire portionsbetween the discharge cells cannot be disregarded. Thus, in theresonance mode based on the series-resonance mode, the wire inductancevalue LN provides the voltage amplification function to the loadresonance transformer 7 (the reactor Lr) provided in series in the powersupply apparatus 10. Thus, the variation range of the load voltage Vdsubjected to the voltage amplification is broadened, and accordingly theplasma load power Pw is determined on the basis of the load voltage Vdapplied to the discharge cells as in Expression (2). Consequently, thevariations in the electric power capacity supplied to the respectivedischarge cells increase, which can cause the breakage of dischargecells in which a large electric power capacity is injected in thedischarge cell portion.

In contrast, it was revealed that, with the power being supplied fromthe parallel-resonance mode power supply apparatus 10 shown in FIG. 11to the plasma generator 5 mentioned above, the load was allowed tooperate stably due to the following factors

In the resonance mode based on the parallel-resonance mode, the voltageamplification function in the load portion is lowered, and accordinglythe current amplification becomes predominant. The load voltage Vdapplied to the discharge cells becomes substantially equal to thetransformer voltage Vs. Even if the wire inductance value LN variesgreatly, the voltage amplification degree associated with the wireinductance value LN becomes much smaller than the voltage amplificationdegree in the series-resonance mode due to the plurality of dischargecells. Thus, the variation range of the load voltage Vd applied to therespective discharge cells is very small. As a result, the variation inthe electric power capacity supplied to the respective discharge cellsis small, and accordingly power is supplied evenly, eliminating thefactor in, for example, the breakage of some discharge cells caused bythe concentration of a large electric power in the discharge cells.

That is, the total load voltage Vd0, which is kept constant, is appliedto the reactor Lr provided in parallel with the transformer 4, providingthe current amplification resonance mode in which the reactive currentIc reflected from the load side is used. This satisfies the conditionfor producing no voltage resonance associated with the wire inductancevalue LN in the connecting wire portions between the discharge cells.Thus, the wire inductance value LN and the load resonance transformer 7(the reactor Lr) provided in the power supply apparatus 10 hardlyinterfere with each other, and accordingly the load voltage Vd appliedto the respective discharge cells is kept substantially constant. Thevariation in the load voltage Vd is small, and accordingly the variationin the electric power capacity that is supplied to the respectivedischarge cell portions and is determined based on the plasma load powerPw in Expression (2) becomes small, producing the above effect.

It was also found that the series-resonance mode and theparallel-resonance mode coexist in the actual power supply apparatus 10due to the configuration of the transformer 4, and the like. Thus, theinventors conducted tests to determine the suitable ratio between theseresonances with a view toward operating the plasma generator 5 stably.

The results of the tests revealed the appropriate configuration, inwhich the parallel reactor component in the output portion of the powersupply apparatus 10 is more than about five times as great as the seriesreactor component. Further, the transformer 4 is designed such that thefunction of the load resonance transformer 7 (or equivalently, thecombined resonance reactor Lr for the transformer 4) is provided to theinside of the transformer 4, and therefore the transformer 4 accordingto the present invention serves as the transformer (high-performancetransformer) dedicated to the plasma generator 5.

In the present embodiment, power supply apparatus 10 is provided in sucha manner that the above-mentioned condition of the resonance ratio issatisfied (or equivalently, the parallel resonance becomes predominant).To be more specific, the new transformer 4 is provided in the presentembodiment, the transformer 4 having the function of the load resonancetransformer such that the above-mentioned condition of the resonanceratio is satisfied. FIG. 13 is a diagram showing a configuration of anequivalent circuit of the new transformer (the high-performancetransformer) 4. FIG. 14 is a diagram showing the performancecharacteristic of the transformer 4.

With reference to FIG. 14, the vertical axis on the left indicates themagnetizing inductance (a given unit), the vertical axis on the rightindicates the leakage inductance (a given unit), the horizontal axisindicates the transformer gap length (mm). A magnetizing inductancecharacteristic Ls2 converted on the secondary side of the transformer 4is denoted by 2001. A leakage inductance characteristic Ld2 converted onthe secondary side of the transformer 4 is denoted by 2002.

FIG. 13 illustrates the equivalent circuit of the new transformer 4 inaddition to the current-limiting reactor Lc described in theembodiment 1. The magnetizing inductance component for forming amagnetic field on the primary-side transformer coil is denoted by Ls1.The leakage inductance component assumed on the basis of the couplingloss of the magnetic flux generated by the primary-side coil and themagnetic flux generated by the secondary-side coil is denoted by Ld2.

The load connected to the secondary side of the transformer is normally,for example, the inductive load such as a motor, a resistive load suchas a thermoelectric apparatus, or the capacitive load such as the plasmagenerator according to the present invention. In general, thetransformer is designed to be compatible with various loads mentionedabove. That is, the normal transformer is optimally designed andproduced under the condition that the reactive (reflection) current Icis absent. Thus, the normal transformer is designed in such a mannerthat the magnetizing inductance component Ls1 is maximized in order tominimize the primary current for magnetization supplied from the primaryside and that the leakage inductance component Ld2 is minimized in orderto increase the degree of magnetic field coupling between theprimary-side coil and the secondary-side coil.

Thus, the normal transformer is designed in such a manner that thetransformer magnetic material core gap (the transformer gap length,hereinafter also referred to as the gap length) falls within a region3001, thus being equal to or less than 0.2 mm (see FIG. 14).

As described above, in the normal transformer, the magnetizinginductance has been the inductance Ls1 formed on the primary side. Incontrast, the new transformer 4 according to the present invention isdesigned in such a manner that, with attention being directed toward theabove-mentioned reactive current Ic flowing to the secondary side of thetransformer 4, the center of focus is the secondary-side magnetizinginductance Ls2 formed in the secondary-side of the transformer 4 by thereactive current Ic.

The present embodiment provides the parallel resonance effect to thesecondary-side magnetizing inductance Ls2 of the transformer 4 and tothe plasma generator 5 on the load side. Thus, the function of the loadresonance transformer 7 can be provided inside the transformer 4,allowing the secondary side of the transformer 4 to perform the parallelresonance with the load.

Further, the new transformer 4 according to the present embodiment isbased on the parallel resonance as described above. That is, the degreeof parallel resonance associated with the relation between themagnetizing inductance Ls2 on the secondary side of the transformer 4and a total capacitance C0 of the plasma generator 5 is set to begreater than the degree of series resonance associated with the relationamong the leakage inductance Ld2 of the transformer 4, thecurrent-limiting reactor Lc provided at the output unit of the inverter3, and the total capacitance C0 of the plasma generator 5. In otherwords, in the transformer 4, the leakage inductance component Ld2 isminimized relative to the magnetizing inductance Ls2 on the secondaryside. In particular, the transformer 4 in FIG. 13 designed to satisfythe relation in the following expression is the new transformer 4according to the present embodiment.

magnetizing inductance on the secondary side Ls2>5·leakage inductanceLd2

That is, in the new transformer 4 according to the present embodiment,the secondary-side magnetizing inductance Ls2 is more than five times asgreat as the leakage inductance Ld2. The inductance value is obtained bysubstituting the capacitance value and the working frequency of the loadinto Expression (1) such that the resonance frequency (Expression (1))falls within the working frequency range of the plasma generator 5. Thecalculated inductance value is given as the transformer inductancevalue.

Through the use of the transformer 4 that satisfies the above-mentionedcondition with a view toward improving the power factor, the majority ofthe above-mentioned reactive current is caused to flow backward to thesecondary-side magnetizing inductance of the transformer 4.

The secondary-side magnetizing inductance Ls2 is adjusted for thetransformer 4 that fulfills the above-mentioned requirement. That is,the gap length of the transformer 4 needs to be greater than the gaplength of the normally used transformer. After the inventors'consideration, it was found that the new transformer 4 according to thepresent embodiment is used with the appropriate gap length being equalto or smaller than 3.5 mm. With consideration given to the actual use ofthe transformer 4, it was found that the gap length of the transformer 4is preferably equal to or greater than 1 mm. Thus, it is appropriatethat the gap length of the new transformer 4 according to the presentembodiment is set within the range of a region 3002 as shown in FIG. 14.

Here, the gap length of the transformer 4 may be greater than 3.5 mm ifthe relation of “magnetizing inductance Ls2 on the secondaryside>5·leakage inductance component Ld2” is satisfied (see FIG. 14). Ina case where the gap length of the transformer 4 is set to be greaterthan 3.5 mm, the leakage flux between the gaps increases, andaccordingly this leakage flux may cause the problems such as the heatgeneration in the components of the power supply apparatus 10. With aview toward smoothly using the power supply apparatus 10, the gap lengthis desirably set to be equal to or smaller than 3.5 mm.

The electric capacitance of the power supply apparatus 10 is decreasedin a case where the gap length of the transformer 4 is set to be smallerthan 1 mm, the magnetizing inductance Ls2 is increased, and theresonance frequency in Expression (1) is set to be constant. However,the downsizing and the price reduction of the power supply apparatus 10can be hardly achieved even if the power supply apparatus 10 having asmall electric capacity is caused to resonate with the load. In view ofthe above-mentioned problems, the gap length of the transformer 4according to the present invention is desirably set to be equal to orgreater than 1.0 mm. This allows the input capacity of the power supplyapparatus 10 to be equal to or greater than 1 kW.

In the present embodiment, to be precise, the working alternatingfrequency (resonance frequency) fc of the power supply apparatus 10 isobtained through circuit calculation on the basis of the inductancecomponent of the current-limiting reactor Lc, the inductance components(such as the leakage inductance and the magnetizing inductance) of thenew transformer 4 according to the present embodiment, and the totalcapacitance C0 of the plasma generator 5. The power supply apparatus 10outputs high-frequency and high-voltage power at the calculated fc tothe plasma generator 5 through the high-performance transformer 4. Inparticular, the controller 6 controls the inverter 3 to work at theresonance frequency fc and output a high-frequency voltage (moreparticularly, the pulse cycle of the inverter 3 is set and the outputvoltage is controlled on the basis of the pulse width of the inverter3).

Here, fc is calculated from Expression (1) mentioned above. A combinedinductance L0 obtained by combining the inductance component of thecurrent-limiting reactor Lc mentioned above and the inductancecomponents of the transformer 4 is denoted by L in Expression (1). Inother words, the combined inductance L0 of the power supply apparatus 10downstream from the output side of the inverter 3 is denoted by L inExpression (1). The combined capacitance C0 of the plasma generator 5 isdenoted by C in Expression (1).

As described above, in the present embodiment, the transformer 4 has thesecondary-side magnetizing inductance Ls2 more than five times as greatas the leakage inductance Ld2. Thus, the power factor of the powersupply apparatus 10 is improved based on the parallel resonance,allowing for the stable resonance action as well as the downsizing andthe cost reduction of the power supply apparatus 10. The plasmagenerator 5 receiving power supply from the power supply apparatus 10can accordingly work very stably.

The description in the present embodiment has been given on the case inwhich the secondary-side magnetizing inductance Ls2 of thehigh-performance transformer 4 is set to be more than five times asgreat as the leakage inductance Ld2 in the power supply apparatus 10that includes the current-limiting reactor Lc and has the function ofstopping in the event of any abnormality and the function of notifyingabnormalities described in the embodiment 1.

This embodiment in which the secondary-side magnetizing inductance Ls2is set to be more than five times as great as the leakage inductance Ld2is applicable to the transformer 4 in the power supply apparatus 10 thatdoes not include the current-limiting reactor Lc and does not have thefunction of stopping in the event of any abnormality and the function ofnotifying abnormalities described in the embodiment 1. This alsoprovides the effect that the parallel resonance action can be performedstably. Similarly, the embodiment in which the secondary-sidemagnetizing inductance Ls2 of the transformer 4 is set to be more thanfive times as great as the leakage inductance Ld2 is applicable to thepower supply apparatus 10 that includes the current-limiting reactor Lcbut does not have the function of stopping in the event of anyabnormality nor the function of notifying abnormalities.

Embodiment 3

In the embodiment 1, the description has been given on the case in whichthe current-limiting reactor Lc is disposed between the output unit ofthe inverter 3 and the input unit of the transformer 4 (see FIG. 1). Inthe present embodiment, the inductance of the primary-side coil of thehigh-performance transformer 4 is also equipped with the function of thecurrent-limiting reactor Lc. Thus, the physical components of thecurrent-limiting reactor Lc can be omitted, and accordingly power supplyapparatus 10 can be configured to include the main circuit that isformed exclusively of the direct-current voltage output unit 20, theinverter portion, and the high-performance transformer 4. Thetransformer 4 according to the present embodiment will be describedbelow.

The primary-side leakage inductance and/or the primary-side magnetizinginductance of the transformer 4 takes over the inductance component ofthe current-limiting reactor Lc such that the transformer 4 is equippedwith the function of the current-limiting reactor Lc. That is, thenumber of turns of the primary-side coil of the transformer 4 isadjusted such that the current-limiting reactor component is taken overby the primary-side leakage inductance and/or the primary-sidemagnetizing inductance.

For example, a magnetic flux φL being a part of a magnetic flux φ0generated in the primary-side coil of the transformer 4 is caused toleak, and accordingly a magnetic flux φ2 linked to the secondary-sidecoil of the transformer 4 is reduced, which increases the primary-sideleakage inductance of the transformer 4. The number of turns of the coilon the primary side is adjusted in such a manner that the amount ofincrease in the primary-side leakage inductance is the current-limitingreactor component.

Thus, in the present embodiment, the transformer 4 is equipped with thefunction of the current-limiting reactor. The physical components of thecurrent-limiting reactor Lc can be accordingly omitted and theshort-circuit current can be regulated by the transformer 4 alone.

Here, the transformer 4 described in the embodiment 1 may be equippedwith the function of the current-limiting reactor or the transformer 4described in an embodiment 2 may be equipped with the current-limitingreactor 4.

Embodiment 4

The present embodiment relates to the improvement in capacity of thepower supply apparatus 10 described in the embodiment 2. The powersupply apparatus 10 according to the present embodiment is effective insupplying electric power to the plasma generator 5 having an increasedcapacity.

As described above, the common transformers installed in the powersupply apparatuses are designed in such a manner that theirspecifications are compatible with various loads such as the inductiveloads, the resistive loads, and the capacitive loads. Thus, theconventional transformer is designed with no consideration given to thevoltage reflection (the reactive current) from the loads during drivingof the power source and with emphasis on minimizing the heat loss of thetransformer itself.

The conditions for the transformer core are determined in such a mannerthat the alternating electric power is supplied while the electric lossis regulated, with the magnetizing impedance on the primary side of thetransformer being increased by maximizing the magnetizing inductancevalue of the transformer and minimizing the leakage inductance of thetransformer. Thus, the conventional transformer has been designed insuch a manner that the gap length is set to be zero or is reduced to aminimum (see the region 3001 in FIG. 14).

Operating these transformers connected in parallel (hereinafter referredto as parallel operation (of the transformers) has drawback ofincreasing variations in current flowing through the respectivetransformers due to the following reasons. The power supply apparatus inwhich the transformers each having a small capacity are connected inparallel has not been in use, and instead, the electric capacity of thepower supply apparatus has been increased by upsizing one transformer.

That is, the normal transformer is designed as the universal transformerthat is compatible with various loads. The normal transformer is thusdesigned to have an increased coil inductance (a very small gap length)with consideration given only to the flux coupling in the transformer.As indicated by the performance characteristic of the transformer inFIG. 14, the design is intended for the region 3001 in which the gaplength of the transformer is small. Although the magnetizing inductancevalue is great in this region, the magnetizing inductance characteristic2001 is very steep. In terms of production accuracy, the variation inthe magnetizing inductance of the individual transformers is as greatas, around ±25%. During the parallel operation of a plurality ofconventional transformers, the variation width of the primarymagnetizing current of the transformer varies by about 50% at maximumdue to the variations in the magnetizing inductance of the individualtransformers. Thus, the parallel operation of the conventionaltransformers results in increased variations in the current supplied tothe individual transformers.

In the conventional transformer, the electric capacity transmitted tothe secondary side of the transformer is dependent on the magnetizingcurrent on the primary side. As described above, the variations in thecurrent for the individual transformers cause a flow of current toconcentrate in one of the transformers during the parallel operation ofthe transformers. The current concentration results in heat generation(heat loss) in the transformer itself. Thus, it is a common practice toavoid the parallel operation of the transformers.

In the present embodiment, meanwhile, the parallel operation of thetransformers is enabled through the use of the transformers according tothe embodiment 2 each having the function of improving the power factor.That is, the electric power to be transmitted to the individualtransformers can be equally distributed even if the electric capacitysupplied to the transformers is increased by the parallel operation ofthe transformers according to the embodiment 2.

In the present invention, the load is limited to the plasma generator 5(or equivalently, the capacitive load). Thus, in the transformer 4according to the embodiment 2, the reactive current Ic reflected fromthe load to the transformer 4 on the power supply apparatus 10 side isused to improve the power factor (see the embodiment 2). The electricpower is accordingly distributed equally to the transformers provided inparallel.

FIG. 15 is a diagram showing the state in which the plurality oftransformers 4 described in the embodiment 2 are connected in parallel.For the brevity of the drawing, FIG. 15 exclusively illustrates theplurality of transformers 4 disposed in the power supply apparatus 10and the current-limiting reactor Lc. Unlike in FIG. 15, thecurrent-limiting reactor Lc may be omitted or the transformer 4 may beequipped with the function of the current-limiting reactor Lc (see theembodiment 3). The transformer 4 is the high-performance transformerhaving the parallel resonance function described in the embodiment 2.

The parallel operation of the transformers 4 will be described below.

The transformers 4 are provided through the use of the magnetizinginductance on the secondary side provided by the reactive current Icreflected from the load side. The current obtained by deducting thereactive current Ic from the current supplied to the primary side flowsthrough the transformers 4, and then is supplied to the plasma generator5. Consequently, the current that is supplied from the primary sides ofthe transformers 4 and flows through the individual transformers 4 (theactive current alone obtained by excluding the reactive current Ic fromthe load) is small. The power factor of the load is improved only bythis small current flowing thought the secondary-side coils of thetransformers 4, thus preventing the transformers from further generatingheat (losing heat).

For the normal transformer, a secondary load voltage Vd2 (kV) isuniquely given on the basis the ratio between the number of turns of theprimary-side coil and the number of turns of the secondary-side coil.Meanwhile, as indicated by the following expression, the secondary-sideload voltage Vd2 (kV) of the transformer 4 described in the presentembodiment is determined on the basis of not only the ratio between thenumber of turns of the primary-side coil and the number of turns of thesecondary-side coil but also the voltage value induced by the reactivecurrent Ic reflected from the load side to the secondary-side coil. Theinduced coil voltage varies depending on the secondary-side magnetizinginductance value of the transformer 4 affected by the flow of thereactive current Ic. The induced voltage value is given by the followingexpression.Vd2=2·π·f·Ls2·Ic

In the above expression, f indicates the resonance frequency, which issubstantially equal to the working frequency because the power supplyapparatus 10 works in this resonance frequency range. The secondary-sidemagnetizing inductance is denoted by Ls2.

The reactive current Ic flows to the individual transformers 4 in such amanner that the secondary-side load voltage Vd2 given by the aboveexpression is kept constant even if the (secondary-side) magnetizinginductance of the transformers 4 varies due to the use of the pluralityof transformers 4 connected in parallel (the transformers 4 areconnected in parallel and Vd2 is therefore at the same potential foreach of the transformer 4).

The high-performance transformer 4 described in the embodiment 2 allowsfor the improvement in the production accuracy of the secondary-sidemagnetizing inductance Ls2. As described in the embodiment 2, thisimprovement is achieved by the greater gap (about several millimeters)in the transformer 4. In particular, the production accuracy of thesecondary-side magnetizing inductance Ls2 for transformer 4 according tothe embodiment 2 is within a±3% range (see the region 3002 in FIG. 14).

The use of the transformers 4 according to the embodiment 2 can keep thevariations in the magnetizing inductance Ls2 on the secondary side amongthe individual transformers 4 to a minimum. Consequently, there issubstantially no variation in the reactive current Ic flowing throughthe individual transformers 4, and therefore the flow of the reactivecurrent Ic is substantially equal for each of the transformers 4. Theamount of electric power supplied from the primary side to the secondaryside of the transformer 4 is equivalent to the active electric poweralone obtained by excluding the amount of reactive electric powersupplied to the load. In the individual transformers 4 connected inparallel, the primary-side voltage and the secondary-side voltage are atthe same potential. Thus, the variations in the active electric powerdistributed among the individual transformers 4 fall within thevariation accuracy for the inductance of the individual coil. Thevariations in the inductance of the individual coil of thehigh-performance transformer 4 fall within the above-mentionedproduction accuracy (about ±3%), and accordingly the active electricpower transmitted from the primary sides to the secondary sides of thetransformers 4 connected in parallel is substantially equal for each ofthe transformers 4. This prevents the thermal damage to the transformers4.

As described above, through the use of the high-performance transformers4 described in the embodiment 2, the parallel operation of thetransformers 4 does not cause excessive heat generation in thetransformers 4. Thus, the parallel operation of the transformers 4 canbe performed and the capacity of the power supply apparatus 10 can beincreased along with an increase in the capacity of the plasma generator5.

Increasing the capacity through the use of one transformer results innot only the upsizing of the transformer but also a significant increasein cost. Meanwhile, the present embodiment allows for the paralleloperation of the transformers 4, so that the power supply apparatus 10can increase in capacity at low cost.

Embodiment 5

In some cases, the amount of electric power input from the power supplyapparatus 10 (the amount of electric power input to the plasma generator5 by the power supply apparatus 10) is made variable such that theconcentration of gas such as the ozone gas generated by the plasmagenerator 5 can be changed. In general, the amount of electric powerinput and the concentration of gas are in one-to-one relationship that agas of higher concentration is generated due to an increase in theamount of electric power input. The amount of electric power inputvaries within a range of 0 to 100% of the rated power of the powersupply apparatus 10.

The following method, which is a prior technique, is an example of thecontrol method for varying the amount of electric power input from thepower supply apparatus 10 to obtain the desired electric power amountvalue and for steadily supplying (inputting) the desired electric poweramount value to the load.

In particular, the high-frequency alternating load current Id0 suppliedto the plasma generator 5 is usually detected. Then, the controller 6changes the control signal of the inverter 3 (the inverter frequency forthe pulse width τ of the inverter) such that the load current Id0reaches the target current value (the current value which provides thedesired electric power value). According to the control method, thealternating current waveforms of the inverter output from the inverter 3are controlled based on the changed control signal.

According to the above-mentioned control method, the inverter 3 has beensubjected to the feedback control system such that the load current Id0reaches the target current value, with the amount of electric powerinput supplied from the power supply apparatus 10 not being regarded asthe direct control amount but with the detected load current Id0 beingregarded as the control amount. That is, in the above-mentioned controlsystem, the amount of electric power input including the reactiveelectric power amount supplied from the power supply apparatus 10 hasbeen variably controlled in an indirect manner.

According to the above-mentioned control method, an electric power inputamount Pw needs to be calculated based on the following expressionusing: the effective load current Id0 having the load current waveformsdetected by the detection unit 41 in FIG. 1; the effective load voltageVd0 having the load voltage waveforms detected by the detection unit 42in FIG. 1; and the load power factor ηd that is dependent on the amountof electric power input.Pw=(effective load current Id0)×(effective load voltage Vd0)×(load powerfactor ηd)=(load current Id0)×(effective load voltage Vd0)×cos φ

The load conditions vary depending on the load voltage applied to theplasma generator 5 and the amount of gas flow supplied to the plasmagenerator 5. It is therefore difficult to accurately obtain, all thetime, the effective current value, the effective voltage, and a phasedifference φ between the load current and the load voltage on the basisof the detected load current signal and the detected load voltage signalvalue according to the method for calculating the electric power inputamount Pw with the above expression. In particular, it is very difficultto obtain the accurate phase difference φ from the effective loadcurrent Id0 and the effective load voltage Vd0 associated with a higherfrequency and a higher voltage. Thus, according to the above-mentionedcontrol method, the electric power input amount Pw is provided with alow accuracy, and it is therefore difficult to keep the electric powerinput amount Pw constant.

The inventors noted the one-to-one correspondence between the amount ofalternating-current electric power input from the power supply apparatus10 to the plasma generator 5 and the amount of direct-current electricpower input to the inverter 3 in the power supply apparatus 10. That is,once the direct-current electric power amount at a low voltage in thepower supply apparatus 10, aside from the high voltage portion of theload, is determined, the amount of electric power input is uniquelygiven in accordance with the direct-current electric power amount (andvice versa). Thus, it was noted that the direct-current electric poweramount is controlled to be constant at the desired value of thedirect-current electric power amount, and accordingly the amount ofelectric power input to the plasma generator 5 is controlled to beconstant at the desired electric power input amount value.

The present embodiment provides the power supply apparatus 10 capable ofkeeping the electric power input amount constant through the feedforwardcontrol and the feedback control, in which the amount of direct-currentelectric power input to the inverter 3 in the power supply apparatus 10is regarded as the direct control value, and stably supplying theelectric power input amount to the plasma generator 5.

Firstly, the user selects the concentration of gas such as an ozone gas,which is generated in the plasma generator 5 through the plasmatreatment (the selection of a desired gas concentration C). That is, theuser inputs the desired concentration C of the above-mentioned gas tothe power supply apparatus 10 according to the present embodiment (theuser may input, instead of the desired concentration C, a targetelectric input amount value Po′, which will be described below, as theamount of electric power input such that the gas of the desiredconcentration C is generated).

Then, the controller 6 calculates a target direct-current electricamount value Po in accordance with the operation conditions of theplasma generator 5 and the desired gas concentration C (or the targetelectric input amount value Po′) (the feedforward control). As is clearfrom the above description, the target electric input amount value Po′is uniquely given on the basis of the target direct-current electricamount value Po. Under the above-mentioned operation conditions of theplasma generator 5, the amount of electric power input equivalent to thetarget electric input amount value Po′ is input to the plasma generator5, and then a gas of the desired concentration C is generated in theplasma generator 5.

Further, the controller 6 determines an inverter frequency fo or aninverter τo on the basis of the target direct-current electric amountvalue Po. Then, the controller 6 performs the control (feedforwardcontrol) over the output from the inverter 3 in accordance with thedetermined inverter frequency fo or the determined inverter pulse widthτo (considered as the inverter control value). The inverter 3 iscontrolled in accordance with fo or τo, so that the amount of electricpower input from the power supply apparatus 10 to the plasma generator 5approaches the target electric input amount value Po′.

Next, the controller 6 detects a direct current Ii and a direct-currentvoltage Vi at the output portion of the direct-current voltage outputunit 20. Here, a current detector 21 shown in FIG. 1 detects the directcurrent Ii whenever necessary and transmits the detected value to thecontroller 6 whenever necessary. Further, a voltage detector 22 shown inFIG. 1 detects the direct-current voltage Vi whenever necessary andtransmits the detected value to the controller 6 whenever necessary. Asshown in FIG. 1, the individual detectors 21 and 22 are disposed betweenthe direct-current voltage output unit 20 and the inverter 3.

Then, the controller 6 calculates a direct-current electric amount valuePi (=Ii×Vi) on the basis of the detection results Ii and Vi. Further,the controller 6 fine-tunes the inverter frequency f or the inverterpulse width τ (considered as the inverter control value) in such amanner that a difference ΔP (=Po−Pi) between the target direct-currentelectric amount value Po and the direct-current electric amount value Pibecomes zero, and the controller 6 performs the control (feedbackcontrol) over the output from the inverter 3 in accordance with theinverter frequency f or the inverter pulse width τ obtained after thefine tuning.

For example, on condition that the target direct-current electric amountvalue Po is greater than the direct-current electric amount value Pi,the inverter frequency f is increased and/or the inverter pulse width τis increased.

The above-mentioned control is performed such that the difference ΔPbecomes zero, and consequently the amount of electric power input to theplasma generator 5 is kept constant at the target electric input amountvalue Po′ mentioned above.

As a result of the above-mentioned control action, the power supplyapparatus 10 controls the amount of electric power input to the plasmagenerator 5, which is the amount dependent on the desired gasconcentration C selected by the user, and keeps the amount constant atthe target electric input amount value Po′.

As described above, power supply apparatus 10 can change the amount ofelectric power input over a range of 0 to 100% of the rated power inaccordance with the desired gas concentration.

The target direct-current electric amount value Po mentioned above iscalculated in the following manner. That is, the controller 6 prestorestables and arithmetic expressions as data. With the tables and thearithmetic expressions, the target direct-current electric amount valuePo is uniquely given and determined depending on the operationconditions of the plasma generator 5 and the desired gas concentrationC.

The values indicating the operation conditions of the plasma generator 5are a gas supply flow rate Q of the source gas, a pressure P in thedischarge cell, a flow rate Qw of the refrigerant flowing through theplasma generator 5, and a temperature Tw of the refrigerant (thephysical quantities described in the embodiment 1). The controller 6acquires, as input data, these values Q, P, Qw, and Tw, which indicatethe operation conditions of the plasma generator 5, from the plasmagenerator 5 through the external signal interface 63.

The controller 6 calculates the target direct-current electric amountvalue Po by applying, as the data for the tables and the arithmeticexpressions mentioned above, the above-mentioned acquired values Q, P,Qw, Tw, and the desired gas concentration C selected and input by theuser.

The controller 6 also presets and prestores, as data, the value of theinverter frequency fo or the value of the inverter pulse width τo, thesevalues being uniquely specified with respect to the targetdirect-current electric amount value Po. As mentioned above, thecontroller 6 can uniquely determine the inverter frequency fo or theinverter pulse width τo with respect to the calculated targetdirect-current electric amount value Po. As described above, theinverter 3 is controlled in accordance with fo or τo, so that the amountof electric power input from the power supply apparatus 10 to the plasmagenerator 5 is approximated to the target electric input amount valuePo′ (fo and τo are values based on theory, and thus are not equal to thetarget electric input amount Po′).

On condition that each of the above-mentioned values Q, P, Qw, and Tw isconstant, the amount of electric power input is kept constant at thetarget electric input amount value Po′ (the amount of direct-currentelectric power input to the inverter 3 is kept constant at the targetdirect-current electric amount value Po), whereby the gas of theconstant desired concentration C mentioned above is generated in theplasma generator 5

The above description has been given on the detection of the directcurrent Ii and the direct-current voltage Vi at the output portion ofthe direct-current voltage output unit 20 through the feedback control.If the output voltage from the direct-current voltage output unit 20 iscontrolled to be a constant voltage, meanwhile, the electric inputamount value Pi (=Ii×constant voltage) can be calculated by detectingonly the direct current Ii at the output portion of the direct-currentvoltage output unit 20 through the feedback control. That is, the amountof electric power input from the power supply apparatus 10 can becontrolled to be constant at the target electric input amount value Po′by performing the feedback control and detecting only the direct currentIi at the output portion of the direct-current voltage output unit 20.

As described above, in the present embodiment, the controller 6 performsthe feedforward control (the calculation of the target direct-currentelectric amount value Po, the determination of the inverter frequency orthe inverter pulse width τo through the use of the target direct-currentelectric amount value Po, and the control over the inverter 3 throughthe use of the inverter frequency fo or the inverter pulse width τo) andthe feedback control (the fine-tuning of the inverter frequency f or aninverter pulse width through the use of the target direct-currentelectric amount value Po and the actual detection results (including atleast the detection results on the direct current) at the output portionof the direct-current voltage output unit 20 and the control overinverter 3 through the use of the inverter frequency f or the inverterpulse width τ obtained after the fine tuning).

That is, in the present embodiment, the power supply apparatus 10detects the direct-current output results from the direct-currentvoltage output unit 20, and the controller 6 performs the feedbackcontrol through the use of the detection results and the targetdirect-current electric amount value Po being the control value suchthat the electric power input amount is kept constant at the targetelectric input amount value Po′ (such that the direct-current electricamount input to the inverter 3 is kept constant at the targetdirect-current electric amount value Po), thus fine-tuning the inverterfrequency f or the inverter pulse width τ.

The feedback control is performed through the use of, for example, thedirect current that is smaller than the load current or the like, andthe direct current or the like and the amount of direct-current electricpower input to the inverter 3 (in other words, the amount of electricpower input) are in one-to-one correspondence (the amount of electricpower input is regarded as the direct control amount value). The amountof electric power input is thus controlled, with a high accuracy, to beconstant at the target electric input amount value Po′ in accordancewith the desired gas concentration. Unlike the load current and thelike, the detected direct current and the like do not carry, forexample, noises (the noises being caused by the inverter 3 and thetransformer 4). Again, the amount of electric power input is thuscontrolled, with a high accuracy, to be constant at the target electricinput amount value Po′ in accordance with the desired gas concentration.Thus, the power supply apparatus can continue to supply the plasmagenerator 5 with the stable electric power.

In the present embodiment, the controller 6 may omit a part of theabove-mentioned feedforward control and perform the above-mentionedfeedback control to control the inverter 3 such that the amount ofelectric power input is kept constant at the target electric inputamount value Po′.

That is, as described above, the controller 6 calculates the targetdirect-current electric amount value Po. Immediately afterward, thecontroller 6 performs the feedback control through the use of thedetection results on the direct current or the like, determines theinverter frequency f or the inverter pulse width τ, and brings theamount of direct-current electric power input to the inverter 3 inagreement with the target electric input amount value Po (in otherwords, brings the amount of electric power input in agreement with thetarget direct-current electric input amount value Po′). In this way, thedetermination of the inverter frequency fo or the inverter pulse widthτo and the control over the inverter 3 through the use of the inverterfrequency fo or the inverter pulse width τo may be omitted. However,such a control may reduce the responsivity, so that much time may berequired for the amount of electric power input to reach the targetvalue.

Thus, as described above, the following action is performed. That is,through the feedforward control, the inverter 3 is controlled inaccordance with the inverter frequency fo or the inverter pulse width τoand the amount of electric power input is brought close to the targetelectric input amount value Po′ (the amount of the direct-currentelectric power is brought close to the target direct-current electricamount value Po). Then, through the feedback control, the inverterfrequency f or the inverter pulse width τ is fine-tuned and the inverter3 is controlled in accordance with the inverter frequency for theinverter pulse width τ.

The feedforward control and the feedback control are combined in thestated order, allowing the amount of electric power input to reach thetarget electric input amount value Po′ in a short time.

The controller 6 may change both or one of the inverter frequency andthe inverter pulse width, and accordingly controls the amount ofelectric power input to be equal to the target electric input amountvalue Po′ (controls the amount of the direct-current electric power tobe equal to the target direct-current electric amount value Po).

The controller 6 that performs the feedforward control and the feedbackcontrol described in the present embodiment is applicable to the powersupply apparatus 10 according to any one of the embodiments 1 to 4mentioned above and is also applicable to the power supply apparatus 10obtained by combining all of the embodiments.

For example, the power supply apparatus 10 may omit the current-limitingreactor described in the embodiment 1 and include the controller 6 andthe inverter 3 that perform the action described in the presentembodiment is performed. Alternatively, the power supply apparatus 10may include, instead of the transformer 4 having the configurationdescribed in the embodiment 2, the common transformer 4 as well as thecontroller 6 and the inverter 3 that perform the action described in thepresent embodiment.

That is, apart from the respective embodiments described above, thepower supply apparatus 10 may implement, by itself, the configuration(the configuration for performing the feedforward control and thefeedback control) described in the present embodiment.

As described in the above-mentioned embodiments, in a case where thepower supply apparatus 10 (more specifically, the inverter 3) is drivenat the constant resonance, the feedforward control and the feedbackcontrol may be performed, with only the inverter pulse width beingvariable, such that the amount of electric power input reaches thetarget electric input amount value Po′.

Embodiment 6

With reference to FIG. 4 mentioned above, the waveform shown on the topcolumn is the alternating-current voltage waveform that is output fromthe inverter 3 and has a rectangular shape. The rectangularalternating-current voltage waveform through the transformer 4 causes asinusoidal high frequency and a sinusoidal high voltage to be suppliedto the plasma generator 5. Here, the amount of production (theconcentration) of the gas or the like generated in the plasma generator5 increases with increasing amount of electric power supplied to theplasma generator 5.

That is, the amount of electric power supplied from the power supplyapparatus 10 to the plasma generator 5 is closely related with theconcentration and the like of the gas generated in the plasma generator5. Thus, for the stable control over the concentration of the gasgenerated in the plasma generator 5, it is important to keep theabove-mentioned amount of electric power to be constant by controllingthe inverter frequency f (the pulse cycle=1/f) or the inverter pulsewidth τ being the control value for the inverter 3 shown in FIG. 4.Here, the amount of electric power is controlled to be constant asdescribed in an embodiment 5.

The load impedance (the concentration of the generated gas) in theplasma generator 5 changes depending on not only the amount of electricpower supplied from the power supply apparatus 10 but also theconditions of the load in the plasma generator 5 (the above-mentioned“operation conditions of the plasma generator 5”). Here, as describedabove, the values indicating the operation conditions of the plasmagenerator 5 are the gas supply flow rate Q of the source gas, thepressure P in the discharge cell, the flow rate Qw of the refrigerantflowing through the plasma generator 5, and the temperature Tw of therefrigerant.

For the stable driving of the plasma generator 5, the above-mentionedvalues Q, P, Qw, and Tw that indicate the operation conditions of theplasma generator 5 need to be managed in such a manner that therespective values hardly vary (are kept substantially constant).However, in actuality, it is difficult to keep the above-mentionedvalues Q, P, Qw, and Tw substantially constant because the respectivevalues Q, P, Qw, and Tw change or greatly vary, in some cases, due tothe disturbance caused by, for example, noises superimposed on signallines.

Thus, as described in the embodiment 1, the controller 6 imports, allthe time, the above-mentioned values Q, P, Qw, and Tw that indicate theoperation conditions of the plasma generator 5 through the transmissionand receipt performed between the power supply apparatus 10 and theplasma generator 5. The controller 6 controls the inverter frequency f(the pulse cycle=1/f) or the inverter pulse width τ being the controlvalue for the inverter 3 in accordance with the respective values Q, P,Qw, and Tw such that the above-mentioned electric amount is controlledto be constant at the appropriate value.

The plasma generator 5 is a capacitive load and usually has a very lowload power factor. To improve the power factor, the resonance means forcreating the resonance state between the power supply apparatus 10 andthe plasma generator 5 is disposed in the power supply apparatus 10 andthe driving frequency (the working frequency) of the inverter 3 is setat around the resonance frequency. The technique for improving the powerfactor may be the invention according to the embodiment 2 or may be theseries-resonance mode power factor improvement means and theparallel-resonance mode power factor improvement means that have beendescribed in the embodiment 2.

The power supply device 10 according to the present embodiment includesany one of the power factor improvement means mentioned above. The powersupply apparatus 10 has the function of automatically determining thedriving frequency of the inverter 3. That is, the power supply apparatus10 has the function of automatically searching for the resonancefrequency.

Firstly, the controller 6 sets the amount of electric power input, theinitial power-supply output frequency, the set gas flow rate, the setgas pressure, the set refrigerant temperature, the set refrigerant flowrate, and the like. The set gas flow rate, the set gas pressure, the setrefrigerant temperature, and the set refrigerant flow rate are outputfrom the controller 6 to the MFC, the APC, and the like in the plasmagenerator 5 through the external signal interface 63.

As described in the embodiment 1, while the plasma generator 5 is inoperation, the gas supply flow rate Q of the source gas, the pressure Pin the discharge cell, the flow rate Qw of the refrigerant flowingthough the plasma generator 5, and the temperature Tw of the refrigerantthat are measurement values (the respective physical quantities beingthe measurement values) are always transmitted from the plasma generator5 to the controller 6 through the external signal interface 63.

Then, as described in the embodiment 1, the controller 6 determineswhether the gas supply flow rate Q falls within the desired rangerelative to the set gas flow rate, whether the pressure P in thedischarge cell falls within the desired range relative to the set gaspressure, whether the flow rate Qw of the refrigerant falls within thedesired range relative to the set refrigerant flow rate, and whether thetemperature Tw of the refrigerant falls within the desired rangerelative to the set refrigerant temperature.

Upon determining the occurrence of abnormalities associated with therespective physical quantities in the plasma generator 5 on the basis ofthe respective determination results, the controller 6 deals with theabnormalities by, for example, stopping the output from the inverter 3as described in the embodiment 1. Further, the controller 6 notifiesthat the abnormality has occurred in the plasma generator 5 (which oneof the physical quantities is abnormal) to the outside.

In the absence of any abnormality in the plasma generator 5 so far, thecontroller 6 uses the voltage value and the current value measured inthe power supply apparatus 10 to determine whether any short circuit hasoccurred in the load (refer the description given with reference toFIGS. 2 and 3).

Upon determining the occurrence of any short circuit on the basis of thedetermination results, the controller 6 stops the output from theinverter 3 as described in the embodiment 1. Further, the controller 6makes a notification of any abnormal spot that causes a short circuit tothe outside.

In the absence of any abnormality or any short circuit so far, thecontroller 6 determines whether the action of the components in thepower supply apparatus 10 is abnormal or normal. Upon determining anyabnormality in the action of the components on the basis of thedetermination results, the controller 6 stops the output from theinverter 3. Further, the controller 6 makes a notification of anycomponent which has been determined to be abnormal to the outside.

In a case where the normality is determined in the respectivedeterminations so far, the following action is performed. Here, thecontroller 6 may omit the action associated with the respectivedeterminations made so far, and start from the following action (thecharacteristic technique according to the present embodiment).

The controller 6 sets the above-mentioned amount of electric powerinput, and then the controller 6 determines whether the amount ofelectric power input is the electric power value equivalent to 100% ofthe rated power of the power supply apparatus 10 or the controller 6determines whether the amount of electric power input is the electricpower value equal to or more than the threshold value % and equal to orless than 100% of the rated power of the power supply apparatus 10.Here, the threshold value % is preset in the controller 6. In a casewhere the threshold value % is 90%, the controller 6 determines whetherthe amount of electric power input is equal to or more than 90% andequal to or less than 100% of the rated power of the power supplyapparatus 10.

The action described below is the action of determining the drivingfrequency of the inverter 3 during the operation of the power supply atthe maximum capacity (or during the operation of the power supply at acapacity close to the maximum capacity) and is, after all, the action ofsetting conditions. Thus, in the initial action stage after theimplementation of the system by connecting the plasma generator 5 to thepower supply apparatus 10, in general, the controller 6 is firstlyinstructed to set the amount of electric power input that is equal to100% of the rated power or is equal to or more than the threshold value% and equal to or less than 100% of the rated power.

In a case where the electric power input amount according to theabove-mentioned setting instruction is equal to 100% of the rated powerof the power supply apparatus 10 (or is equal to or more than thethreshold value % and equal to or less than 100% of the rated power ofthe power supply apparatus 10), the controller 6 changes the inverterfrequency f being the control value for the inverter 3 whenevernecessary, and accordingly controls the output from the inverter 3 onthe basis of each of the inverter frequencies f.

Here, the controller 6 causes the inverter frequency f to change (sweep)over the predetermined frequency range (for example, a range of ±2 kHz)with the initial power-supply output frequency set as described abovebeing at the center. Alternatively, the inverter frequency f may becaused to sweep across the entire frequency range. If the sweep range islimited as described above, the time required to find the resonancefrequency can be reduced.

In the implementation stage of the system by connecting the power supplyapparatus 10 and the plasma generator 5, the resonance frequency at thetheoretical value is calculated from Expression (1) mentioned above (thecombined inductance of the power supply apparatus 10 downstream from theoutput side of the inverter 3 is denoted by L in Expression (1) and thecombined capacitance of the plasma generator 5 is denoted by C inExpression (1). With a view toward reducing the time required to findthe resonance frequency, the value calculated from Expression (1) is setfor the controller 6 as the initial power-supply output frequencymentioned above and the controller 6 causes the inverter frequency f tochange (sweep) over the predetermined frequency range with the initialpower-supply output frequency being at the center (for example, causesthe inverter frequency f to change discretely).

In changing the inverter frequency f, the controller 6 also changes theinverter pulse width τ in accordance with changes in the inverterfrequency f so as to satisfy the electric power input amount accordingto the setting instruction, and then transmits the inverter pulse widthτ as the control value to the inverter 3.

The controller 6 changes the inverter frequency f and obtains theinverter output power factor for each of the inverter frequencies f onthe basis of the electricity amount acquired from the detection units 31and 32. The electricity amount refers to the value associated with theelectricity on the output side of the inverter 3, the electricity beingused to obtain the inverter output power factor.

In particular, the current detector 31 shown in FIG. 1 detects theeffective current value at the output unit of the inverter 3 for each ofthe inverter frequencies f subjected to the sweep, and then transmitsthe detection results to the controller 6. The voltage detector 32 shownin FIG. 1 detects the effective voltage value at the output unit ofinverter 3, and then transmits the detection results to the controller6. The controller 6 obtains the active power at the output unit of theinverter 3 from the above-mentioned effective current value and theabove-mentioned effective voltage value for each of the inverterfrequencies f subjected to the sweep.

Then, through the use of the above-mentioned effective current value,the above-mentioned effective voltage value, and the above-mentionedactive power, the controller 6 computes the inverter output power factorη at the output unit of the inverter 3 for each of the inverterfrequencies f subjected to the sweep. Here, assume that the inverteroutput power factor η={(active power)/(effective current value×effectivevoltage value)}×100(%).

FIG. 16 is a diagram showing the state in which the inverter frequency fis caused to change (sweep) in the predetermined frequency range and theinverter output power factor 11 obtained for each of the inverterfrequencies f changes. The vertical axis of FIG. 16 indicates theinverter output power factor η (%) and the lateral axis of FIG. 16indicates the inverter frequency f (kHz).

As shown in FIG. 16, the inverter output power factor 11 is obtained foreach of the inverter frequencies subjected to the sweep, and then thecontroller 6 detects a maximum inverter output power factor ηmax that isthe maximum value among the obtained inverter output power factors η.Then, the controller 6 determines, as the driving frequency fc of theinverter 3, the inverter frequency (being the resonance frequency fc,see fc in FIG. 16) obtained at the maximum inverter output power factorηmax.

After determining the driving frequency fc, the controller 6 transmitsthe driving frequency fc as the inverter frequency f to the inverter 3.Further, the controller 6 transmits, to the inverter 3, an inverterpulse width τc determined on the basis of the driving frequency fc andthe electric power input amount that has been set as described above.

Consequently, a high-frequency waveform based on the driving frequencyfc and the inverter pulse width τc is output from the inverter 3, andthe load power corresponding to the electric power input amount that hasbeen set as described above is supplied to the plasma generator 5.

In some cases, the user needs to change the concentration of the gasgenerated in the plasma generator 5 or to change the above-mentionedvalues (the respective physical quantities) Q, P, Qw, and Tw thatindicate the operation conditions of the plasma generator 5 whilekeeping the concentration of the generated gas unchanged. In such acase, the user changes the amount of electric power input from the powersupply apparatus 10 in accordance with the desired amount of change.

Assume that the user accordingly changes the electric power input amountset to the power supply apparatus 10.

In response to the change, the controller 6 determines whether thechanged amount of the electric power input is equivalent to the electricpower input value that is less than 100% of the rated power of the powersupply apparatus 10 or the controller 6 determines whether the changedamount of the electric power input is equivalent to the electric powerinput value that is less than the above-mentioned threshold value % ofthe rated power of the power supply apparatus 10.

Here, assume that the changed amount of electric power input is lessthan 100% of the rated power (or less than the above-mentioned thresholdvalue % of the rated power). The controller 6 accordingly determinesthat the changed amount of electric power input is less than 100% of therated power (or less than the above-mentioned threshold value % of therated power) of the power supply apparatus 10.

Thus, the controller 6 transmits the driving frequency fc as theinverter frequency f to the inverter 3. In other words, the inverterfrequency f is fixed at the driving frequency fc mentioned above even ifthe instructions to change the amount of electric power input are given.Further, the controller 6 transmits, to the inverter 3, an inverterpulse width τr determined on the basis of the changed amount of electricpower input and the driving frequency fc.

Consequently, a high-frequency waveform based on the driving frequencyfc and the inverter pulse width τr is output from the inverter 3, andthe load power corresponding to the changed amount of electric powerinput is supplied to the plasma generator 5.

From that point forward, even if the power supply apparatus 10 isinstructed to change the amount of electric power input, the controller6 continues to fixedly output the driving frequency fc as the inverterfrequency f to the inverter 3 as long as the changed amount of electricpower input is less than 100% of the rated power (or less than theabove-mentioned threshold value % of the rated power). The inverterpulse width τ is changed as occasion arises in accordance with thechanged amount of electric power input.

There is a possibility that the changed amount of electric power inputis equal to 100% of the rated power (or is equal to or more than theabove-mentioned threshold value % and equal to or less than 100% of therated power). In this case, the power supply apparatus 10 performs thefollowing action.

The power supply apparatus 10 includes a switching unit (not shown inFIG. 1 and the like) capable of selecting whether to redetermine theresonance frequency obtained as described above.

Once the system including the power supply apparatus 10 and the plasmagenerator 5 is implemented, the resonance frequency can hardly change.The user accordingly operates the switching unit to select theinexecution of redetermination of the driving frequency.

In this case, the controller 6 transmits, as the inverter frequency f,the driving frequency fc obtained as described above to the inverter 3.That is, even if the amount of electric power input equal to 100% of therated power (or the amount equal to or more than the above-mentionedthreshold value % and equal to or less than 100% of the rated power) isinstructed and set again, the inverter frequency f is fixed at thedriving frequency fc mentioned above. Further, the controller 6transmits, to the inverter 3, the inverter pulse width τc determined onthe basis of the driving frequency fc and the electric power inputamount that has been set as described above.

Consequently, a high-frequency waveform based on the driving frequencyfc and the inverter pulse width τc is output from the inverter 3, andthe load power corresponding to the electric power input amount that hasbeen set as described above is supplied to the plasma generator 5.

Meanwhile, the resonance frequency is changed in a case where: theplasma generator 5 has been used for a long period of time; the plasmagenerator 5 or the power supply apparatus 10 has undergone designchanges or the like; changes have been made to wires connecting theplasma generator 5 and the power supply apparatus 10 or to wires insidethe plasma generator 5 and the power supply apparatus 10. Thus, there isa possibility that the user operates the switching unit to select theexecution of redetermination of the driving frequency.

In this selection, if the changed amount of electric power input isequal to 100% or the rated power (or is equal to or more than theabove-mentioned threshold value % and equal to or less than 100% of therated power), the power supply apparatus 10 again performs the action ofdetermining the driving frequency in response to the setting of theamount of electric power input (the action being similar to the actionof causing above-mentioned sweep of the inverter frequency and obtainingthe inverter frequency (the resonance frequency) at the maximum inverteroutput power factor ηmax). Assuming that a driving frequency fc′ isdetermined as a result of the determination action, from that pointforward, the controller 6 replaces the above-mentioned driving frequencyfc with the new driving frequency fc′ and performs the action same asthe action described above in response to any change in the electricpower input amount set to the power supply apparatus 10 (the actionbeing similar to the action of the controller 6 that continues tofixedly output the driving frequency as the inverter frequency f to theinverter 3 in response to any change in the electric power inputamount).

The output from the inverter 3 is controlled based on theabove-mentioned driving frequencies fc and fc′ as well as the inverterpulse width obtained as described above. Here, the controller 6 mayfine-tune the inverter pulse width through, for example, the feedbackcontrol described in the embodiment 5 such that the amount of electricpower input is controlled with a high accuracy.

As described above, after the implementation of the system including thepower supply apparatus 10 and the plasma generator 5, the power supplyapparatus 10 according to the present embodiment automaticallydetermines the driving frequency fc in response to the initialinstruction to set, as the amount of electric power input, the valueequal to 100% of the rated power or the value equal to or more than thethreshold value % and equal to or less than 100% of the rated power.

Thus, during the operation of the power supply at the maximum capacity(or during the operation of the power supply at a capacity close to themaximum capacity), the power supply apparatus 10 can be driven at thedriving frequency (resonance frequency) fc with the improved inverteroutput power factor Here, the driving frequency fc is automaticallyprovided depending on models of the plasma generators 5 and productionlot variations.

In the power supply apparatus 10 according to the present embodiment,after the driving frequency fc is obtained, the controller 6 fixedlyoutputs, to the inverter 3, the driving frequency fc obtained asdescribed above in response to the instruction to set, as the amount ofelectric power input, the value less than 100% of the rated power or thevalue less than the threshold value % of the rated power, andaccordingly.

This prevents the action of obtaining the driving frequency every timethe amount of electric power input is changed, thus preventingdeterioration of the processing performance of the power supplyapparatus 10.

Even if the amount of electric power input is changed, there is not muchdifference between the true resonance frequency corresponding to theamount of electric power input and the previously obtained driving(resonance) frequency fc. Due to the difference between the trueresonance frequency and the previously obtained driving (resonance)frequency fc, the inverter output power factor η becomes somewhatsmaller than the maximum inverter output power factor ηmax.

In a case where the amount of electric power input is less than 100% ofthe rated power or is less than the threshold value % of the ratedpower, meanwhile, the power supply apparatus 10 has a capacity inreserve. Assuming that the amount of electric power input is less than100% of the rated power or less than the threshold value % of the ratedpower, the controller 6 possibly controls the inverter 3 at the drivingfrequency fc mentioned above, and accordingly the inverter output powerfactor η could be somewhat smaller than the maximum inverter outputpower factor ηmax, but the power supply apparatus 10 can operate withoutany problem in terms of its performance.

The power supply apparatus 10 according to the present embodimentincludes the switching unit capable of making the above-mentionedselection. In the event of circumstances causing any change in theresonance frequency in the system including the power supply apparatus10 and the plasma generator 5, the controller 6 can automaticallydetermines the proper driving frequency once again in accordance withthe user's request.

Unlike the above description, there is a possibility that the amount ofelectric power input according to the initial setting instruction is notequal to 100% of the rated power of the power supply apparatus 10 (or isneither equal to or more than the threshold value % nor equal to or lessthan 100% of the rated power of the power supply apparatus 10)

In this case, the controller 6 determines the inverter frequency f asthe initial power-supply output frequency that has been set as describedabove. Further, the controller 6 obtains the inverter pulse width τ fromthe electric power input amount that has been set as described above andthe initial power-supply output frequency that has been determined asdescribed above. Then, the controller 6 transmits, to inverter 3, theset initial power-supply output frequency and the obtained inverterpulse width.

Consequently, a high-frequency waveform based on the set initialpower-supply output frequency and the obtained inverter pulse width isoutput from the inverter 3, and the load power corresponding to theelectric power input amount that has been set as described above issupplied to the plasma generator 5.

Then, the electric power input amount set for the power supply apparatus10 is changed. When the set amount of electric power input reaches 100%of the rated power of the power supply apparatus 10 (becomes equal to ormore than the threshold value % and equal to or less than 100% of therated power of the power supply apparatus 10) for the first time, thecontroller 6 performs the action of obtaining the driving frequency fcmentioned above. From that point forward, the action same as the onedescribed above is performed in response to any change in the amount ofelectric power input (the action being similar to, for example theaction of the controller 6 that continues to fixedly output the drivingfrequency fc as the inverter frequency f to the inverter 3 in responseto any change in the amount of electric power input).

The characteristic techniques according to the present embodiment (theautomatic determination of the driving frequency, the fixed outputtingof the driving frequency in response to any change in the amount ofelectric power input, and the like) may be combined with theabove-mentioned embodiments 1 to 5. Alternatively, the power supplyapparatus 10 may be certainly configured to employ the characteristictechnique according to the present embodiment.

Embodiment 7

In the embodiment 6, the power supply apparatus 10 includes the powerfactor improvement means, causes resonances through the use of thereflection current from the load side (the plasma generator 5 side), andautomatically determines the driving frequency. In the embodiment 6, thedriving frequency is equivalent to the inverter frequency (in otherwords, the resonance frequency) at the maximum inverter output powerfactor ηmax.

When the impedance of the load is investigated based on the output fromthe transformer 4 of the power supply apparatus 10 with resonances beingcaused through the use of the reflection current as described above, theinductive impedance of the power factor improvement means mentionedabove and the capacitive impedance on the load side cancel out eachother. If the driving frequency of the power supply apparatus 10 is setat the resonance frequency fc, the above-mentioned inductive impedanceand the capacitive impedance on the load side cancel out each other,providing 0Ω. Consequently, the total discharge plasma impedance(resistance) Rp0 (Ω) alone is left for the plasma generator 5.

If the number n of discharge cells connected in parallel is small, Rp0that is inversely proportional to n has a greater value. Thus, the totalload current Id0 in the plasma generator 5 is regulated, and accordinglya Q value indicating the amplification degree of resonance (in otherwords, the characteristic of the inverter output power factor η shown inFIG. 16) changes gently even if the inverter frequency changes, allowingfor the power supply apparatus 10 to work stably at the resonancefrequency.

In contrast, if the number n of discharge cells connected in parallel isgreat or the discharge resistance of the discharge cells in the plasmagenerator 5 is very small, Rp0 has a very small value. Thus, the totalload current Id0 in the plasma generator 5 becomes extremely great, andaccordingly the Q value indicating the amplification degree of resonance(in other words, the characteristic of the inverter output power factorη shown in FIG. 17) changes steeply in response to any change in theinverter frequency. In this situation, driving the power supplyapparatus 10 driven at the resonance frequency causes, not only anincrease in the reflection current from the load but also a greatincrease in the rate of temporal change in current, thus inducing theoscillation mode in the resonance system.

The oscillation mode becomes a cause of an increase in noise in thepower supply apparatus 10. Such an incase in noise causes, in somecases, electric damage to the electric components in the power supplyapparatus 10, malfunctioning of the power supply apparatus 10, andbreakage of the plasma generator 5.

Thus, in the present embodiment, instead of the actual resonancefrequency, the resonance frequency fc is used to determine the drivingfrequency determined in the embodiment 6.

In particular, as in the embodiment 6, the controller 6 determines theinverter frequency (in other words, the resonance frequency fc) at themaximum inverter output power factor ηmax obtained due to the sweep ofthe inverter frequency. Then, the controller 6 determines the valueobtained by shifting the resonance frequency fc by a micro frequency Δfas the driving frequency (=fc±Δf).

Here, the micro frequency Δf is individually determined depending on theconfiguration of the plasma generator 5 in the actual use. The systemincluding the power supply apparatus 10 and the plasma generator 5 isexperimentally operated in advance at around the resonance frequency fc.This experimental operation provides the determination that theresonance frequency fc is shifted positively or that the resonancefrequency fc is shifted negatively. Then, this experimental operationprovides the determination of the proper micro frequency Δf that allowsfor the stable operation. The micro frequency Δf is preset in thecontroller 6 before the power supply apparatus 10 starts working.

The range of the micro frequency may be determined through theexperimental operation mentioned above and the determined range of themicro frequency may be preset in the controller 6. In this case, thedriving frequency is determined so as to fall within the followingrange. For example, with the inverter frequency being shifted negativelyrelative to the resonance frequency fc, the lower-limit frequency valuethat allows for the normal operation is denoted by Δfr1. With theinverter frequency being shifted positively relative to the resonancefrequency fc, meanwhile, the upper-limit frequency value that allows forthe normal operation is denoted by Δfr2. In this case, any value thatfalls within the range given by the following expression is determinedas the driving frequency. That is, fc−Δfr1≦driving frequency≦fc+Δfr2(see FIG. 17). Note that the resonance frequency fc itself is notconsidered as the driving frequency in the present embodiment (see FIG.17).

As described above, in the present embodiment, the controller 6determines the driving frequency in such a manner that the resonancefrequency fc is left out. This allows for the power supply apparatus 10to operate stably by avoid working operation at the frequency band inwhich the oscillation mode can be induced.

The above description has been given on the technique for stabilizingthe load output unit of the power supply apparatus 10 dedicated to thecapacitive load apparatus. The unit 20 of the power supply apparatus 10that outputs a direct-current voltage may be a converter that rectifiesthe commercial alternating-current voltage and transforms the voltageinto a direct-current voltage or may be a battery (for example, alarge-capacity battery bank configured to include a multistage ormulti-parallel connection), such as a storage battery, capable ofoutputting a direct-current voltage.

In a case where the direct-current voltage output unit 20 is alarge-capacity battery bank, the equivalent circuit in the partcorresponding to the battery includes a voltage source and a capacitivecapacitor. Thus, in some cases, the current reflected on thelarge-capacity battery bank side is subjected to the voltageamplification due to the wire reactor LN in response to the voltageoutput from the large-capacity battery bank, whereby an over voltage maybe reflected to the large-capacity battery bank. This could interferewith the stable operation of the large-capacity battery bank.

The stable driving of the large-capacity battery bank requires atechnique for preventing the reflection of an overvoltage to thelarge-capacity battery bank. One example of such a technique is thetechnique for improving the power factor through the interposed parallelreactors provided for the capacitive load as described in the embodiment2 and the like. The similar technique is used to interpose the parallelreactors in the large-capacity battery bank. The interaction between thecapacitance value in the large-capacity battery bank and the inductancevalue in the wire reactor portion regulates the effect that subjects thereflection current to the series resonance (voltage amplification),thereby diverting the reflected reactive current through the parallelreactors.

The power supply apparatuses 10 described in the respective embodimentsmentioned above are applicable as the power supply apparatuses dedicatedto the capacitive load apparatuses used in the field of semiconductormanufacturing apparatuses such as ozone generators and radicalgenerators. Further, the power supply apparatuses 10 can be used as thepower supply apparatuses for the discharge apparatuses in the field oflaser apparatuses and for the capacitive load apparatuses, such asvery-large-scale ozone generators used in the field of pulp breaching,the field of water treatment, or the field of chemical plant.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention. Further, the invention including only a characteristic partof the invention according to the individual embodiment mentioned aboveand the arbitrary combination of characteristic parts of the inventionsaccording to the individual embodiments can be devised without departingfrom the scope of the invention.

The invention claimed is:
 1. A power supply apparatus that outputs analternating-current voltage to a plasma generator being a capacitiveload including a plurality of discharge cells connected to one another,said power supply apparatus comprising: an inverter that convertsdirect-current electric power to alternating-current electric power;control circuitry that controls said inverter; and a current detectorthat detects a direct current input to said inverter, wherein saidcontrol circuitry (A) determines a target direct-current electric amountvalue in accordance with an external input, and (B) performs feedbackcontrol over said inverter on the basis of at least the direct currentdetected by said current detector in such a manner that an amount of thedirect-current electric power input to said inverter reaches said targetdirect-current electric amount value.
 2. The power supply apparatusaccording to claim 1, wherein a direct-current voltage input to saidinverter is constant, and said control circuitry performs said feedbackcontrol in said (B) on the basis of only the direct current detected bysaid current detector in such a manner that the amount of thedirect-current electric power input to said inverter reaches said targetdirect-current electric amount value.
 3. The power supply apparatusaccording to claim 1, wherein said control circuitry performs saidfeedback control in said (B) on the basis of the direct current detectedby said current detector and a direct-current voltage detected by avoltage detector in such a manner that the amount of the direct-currentelectric power input to said inverter reaches said target direct-currentelectric amount value.
 4. The power supply apparatus according to claim1, wherein said control circuitry (C) determines a first invertercontrol value in accordance with said target direct-current electricamount value, and (D) controls said inverter on the basis of said firstinverter control value and performs said (B) after said (D).
 5. Thepower supply apparatus according to claim 4, wherein said (B) is saidfeedback control performed by adjusting a second inverter control valuein such a manner that the amount of the direct-current electric powerinput to said inverter reaches said target direct-current electricamount value.
 6. The power supply apparatus according to claim 5,wherein said first inverter control value and said second inverter valuecomprise an inverter pulse frequency and an inverter pulse width.
 7. Thepower supply apparatus according to claim 5, wherein said first invertercontrol value and said second inverter control value each comprise aninverter pulse width.
 8. The power supply apparatus according to claim1, wherein said control circuitry calculates the amount of thedirect-current electric power input to said inverter on the basis of thedirect current detected by said current detector and a direct-currentvoltage input to said inverter.
 9. A power supply apparatus foroutputting an alternating-current voltage to a plasma generator, saidpower supply apparatus comprising: an inverter that convertsdirect-current electric power to alternating-current electric power; acurrent detector that detects a direct current input to the inverter;and control circuitry configured to determine a target direct-currentelectric amount value in accordance with an external input, determine anamount of the direct-current electric power input to the inverter basedon the direct current detected by the current detector, and control theinverter according to a difference between the amount of thedirect-current electric power input to the inverter and the targetdirect-current electric amount value.
 10. The power supply apparatusaccording to claim 9, wherein the control circuitry is configured todetermine the amount of the direct-current electric power input to theinverter based on the direct current detected by the current detectorand a direct-current voltage input to the inverter.
 11. The power supplyapparatus according to claim 10, further comprising: a voltage detectorthat detects the direct-current voltage.
 12. The power supply apparatusaccording to claim 10, wherein the direct-current voltage is apredetermined fixed amount.